Categorical take fill value
Closes https://github.com/pandas-dev/pandas/issues/23296
Hello @TomAugspurger! Thanks for updating the PR.

 - There are no PEP8 issues in the file [`pandas/core/arrays/categorical.py`](https://github.com/TomAugspurger/pandas/blob/fb64335479f7a3ec13db7decf55c77448857b2bc/pandas/core/arrays/categorical.py) !

 - There are no PEP8 issues in the file [`pandas/tests/arrays/categorical/test_algos.py`](https://github.com/TomAugspurger/pandas/blob/fb64335479f7a3ec13db7decf55c77448857b2bc/pandas/tests/arrays/categorical/test_algos.py) !



##### Comment last updated on October 23, 2018 at 14:07 Hours UTC Ah, forgot to revert a change. 1 sec. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23297?src=pr&el=h1) Report
> Merging [#23297](https://codecov.io/gh/pandas-dev/pandas/pull/23297?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/5a0c91e5a5bc61c71da08d6968d973255829678d?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/23297/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23297?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #23297      +/-   ##
==========================================
+ Coverage   92.22%   92.22%   +<.01%     
==========================================
  Files         169      169              
  Lines       50897    50903       +6     
==========================================
+ Hits        46940    46946       +6     
  Misses       3957     3957
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.65% <100%> (ø)` | :arrow_up: |
| #single | `42.29% <28.57%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/23297?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/arrays/categorical.py](https://codecov.io/gh/pandas-dev/pandas/pull/23297/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2NhdGVnb3JpY2FsLnB5) | `95.56% <100%> (+0.03%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23297?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/23297?src=pr&el=footer). Last update [5a0c91e...fb64335](https://codecov.io/gh/pandas-dev/pandas/pull/23297?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
