CLN: ASV join_merge
Flake8'd, utilized `param`s to add some additional benchmarks, and simplified the setup where possible. 

```
$ asv dev -b ^join_merge
· Discovering benchmarks
· Running 30 total benchmarks (1 commits * 1 environments * 30 benchmarks)
[  0.00%] ·· Building for existing-py_home_matt_anaconda_envs_pandas_dev_bin_python
[  0.00%] ·· Benchmarking existing-py_home_matt_anaconda_envs_pandas_dev_bin_python
[  3.33%] ··· Running join_merge.Align.time_series_align_int64_index      672ms
[  6.67%] ··· Running ...erge.Align.time_series_align_left_monotonic      203ms
[ 10.00%] ··· Running join_merge.Append.time_append_homogenous           1.57ms
[ 10.00%] ····· /home/matt/Projects/pandas-mroeschke/asv_bench/benchmarks/join_merge.py:29: FutureWarning: consolidate is deprecated and will be removed in a future release.
                self.mdf1.consolidate(inplace=True)

[ 13.33%] ··· Running join_merge.Append.time_append_mixed                2.51ms
[ 13.33%] ····· /home/matt/Projects/pandas-mroeschke/asv_bench/benchmarks/join_merge.py:29: FutureWarning: consolidate is deprecated and will be removed in a future release.
                self.mdf1.consolidate(inplace=True)

[ 16.67%] ··· Running join_merge.Concat.time_concat_empty_left               ok
[ 16.67%] ···· 
               ====== =======
                axis         
               ------ -------
                 0     425μs 
                 1     475μs 
               ====== =======

[ 20.00%] ··· Running join_merge.Concat.time_concat_empty_right              ok
[ 20.00%] ···· 
               ====== =======
                axis         
               ------ -------
                 0     406μs 
                 1     481μs 
               ====== =======

[ 23.33%] ··· Running join_merge.Concat.time_concat_series                   ok
[ 23.33%] ···· 
               ====== ========
                axis          
               ------ --------
                 0     27.5ms 
                 1     218ms  
               ====== ========

[ 26.67%] ··· Running join_merge.Concat.time_concat_small_frames             ok
[ 26.67%] ···· 
               ====== ========
                axis          
               ------ --------
                 0     107ms  
                 1     81.2ms 
               ====== ========

[ 30.00%] ··· Running join_merge.ConcatDataFrames.time_c_ordered             ok
[ 30.00%] ···· 
               ====== ======= =======
               --       ignore_index 
               ------ ---------------
                axis    True   False 
               ====== ======= =======
                 0     146ms   141ms 
                 1     225ms   226ms 
               ====== ======= =======

[ 33.33%] ··· Running join_merge.ConcatDataFrames.time_f_ordered             ok
[ 33.33%] ···· 
               ====== ======= =======
               --       ignore_index 
               ------ ---------------
                axis    True   False 
               ====== ======= =======
                 0     173ms   175ms 
                 1     161ms   155ms 
               ====== ======= =======

[ 36.67%] ··· Running join_merge.ConcatPanels.time_c_ordered                 ok
[ 36.67%] ···· 
               ====== ======= =======
               --       ignore_index 
               ------ ---------------
                axis    True   False 
               ====== ======= =======
                 0     318ms   314ms 
                 1     359ms   363ms 
                 2     1.67s   1.66s 
               ====== ======= =======

[ 40.00%] ··· Running join_merge.ConcatPanels.time_f_ordered                 ok
[ 40.00%] ···· 
               ====== ======= =======
               --       ignore_index 
               ------ ---------------
                axis    True   False 
               ====== ======= =======
                 0     666ms   666ms 
                 1     321ms   297ms 
                 2     297ms   299ms 
               ====== ======= =======

[ 43.33%] ··· Running join_merge.I8Merge.time_i8merge                        ok
[ 43.33%] ···· 
               ======= =======
                 how          
               ------- -------
                inner   1.62s 
                outer   1.61s 
                 left   1.62s 
                right   1.62s 
               ======= =======

[ 46.67%] ··· Running ..._merge.Join.time_join_dataframe_index_multi         ok
[ 46.67%] ···· 
               ======= ========
                 sort          
               ------- --------
                 True   53.0ms 
                False   41.9ms 
               ======= ========

[ 50.00%] ··· Running ...oin_dataframe_index_shuffle_key_bigger_sort         ok
[ 50.00%] ···· 
               ======= ========
                 sort          
               ------- --------
                 True   36.5ms 
                False   29.8ms 
               ======= ========

[ 53.33%] ··· Running ...time_join_dataframe_index_single_key_bigger         ok
[ 53.33%] ···· 
               ======= ========
                 sort          
               ------- --------
                 True   36.6ms 
                False   30.8ms 
               ======= ========

[ 56.67%] ··· Running ....time_join_dataframe_index_single_key_small         ok
[ 56.67%] ···· 
               ======= ========
                 sort          
               ------- --------
                 True   30.6ms 
                False   27.6ms 
               ======= ========

[ 60.00%] ··· Running ..._merge.JoinIndex.time_left_outer_join_index      4.82s
[ 63.33%] ··· Running ...ge.JoinNonUnique.time_join_non_unique_equal      417ms
[ 66.67%] ··· Running join_merge.Merge.time_merge_2intkey                    ok
[ 66.67%] ···· 
               ======= ========
                 sort          
               ------- --------
                 True   72.6ms 
                False   40.9ms 
               ======= ========

[ 70.00%] ··· Running ...rge.Merge.time_merge_dataframe_integer_2key         ok
[ 70.00%] ···· 
               ======= ========
                 sort          
               ------- --------
                 True   23.3ms 
                False   10.0ms 
               ======= ========

[ 73.33%] ··· Running ...erge.Merge.time_merge_dataframe_integer_key         ok
[ 73.33%] ···· 
               ======= ========
                 sort          
               ------- --------
                 True   5.46ms 
                False   4.87ms 
               ======= ========

[ 76.67%] ··· Running join_merge.MergeAsof.time_by_int                   48.6ms
[ 80.00%] ··· Running join_merge.MergeAsof.time_by_object                83.9ms
[ 83.33%] ··· Running join_merge.MergeAsof.time_multiby                   1.32s
[ 86.67%] ··· Running join_merge.MergeAsof.time_on_int                   29.2ms
[ 90.00%] ··· Running join_merge.MergeAsof.time_on_int32                 33.9ms
[ 93.33%] ··· Running join_merge.MergeCategoricals.time_merge_cat         775ms
[ 96.67%] ··· Running join_merge.MergeCategoricals.time_merge_object      1.50s
[100.00%] ··· Running join_merge.MergeOrdered.time_merge_ordered          146ms
```

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18917?src=pr&el=h1) Report
> Merging [#18917](https://codecov.io/gh/pandas-dev/pandas/pull/18917?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/6164da24a7d3f9469fcad8b987c9c7fac1c8dd25?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18917/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&height=150&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/18917?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #18917   +/-   ##
=======================================
  Coverage   91.65%   91.65%           
=======================================
  Files         154      154           
  Lines       51368    51368           
=======================================
  Hits        47080    47080           
  Misses       4288     4288
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.52% <ø> (ø)` | :arrow_up: |
| #single | `40.84% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18917?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18917?src=pr&el=footer). Last update [6164da2...12e86cc](https://codecov.io/gh/pandas-dev/pandas/pull/18917?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!