Fix/read csv utf aliases
- [x] closes #13549 
- [x] tests added / passed
- [x] passes `git diff upstream/master | flake8 --diff`
- [x] whatsnew entry

-read_csv with engine=c throws error when encoding=UTF_16 (anything other than utf-16)
-improved nosetests and moved to in pandas/io/tests/common.py
-passes `pep8radius upstream/master --diff` and  `git diff upstream/master | flake8 --diff`
-put what's new entry in 0.19.0 in accordance with milestone posted on issue

@nateGeorge Now there is only a lint error left (reason for the travis failure):

```
pandas/io/tests/parser/common.py:21:1: F811 redefinition of unused 'BytesIO' from line 11
```
 ## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/14060?src=pr) is 85.27% (diff: 100%)

> Merging [#14060](https://codecov.io/gh/pydata/pandas/pull/14060?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will increase coverage by **<.01%**

``` diff
@@             master     #14060   diff @@
==========================================
  Files           139        139          
  Lines         50446      50449     +3   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits          43018      43021     +3   
  Misses         7428       7428          
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [df2d9ab...aca4148](https://codecov.io/gh/pydata/pandas/compare/df2d9ab917a1ef4732cfb6c3317432f60c071074...aca41484fbdd3a2d26f95286242e31e29a254665?src=pr)
 @nateGeorge Thanks!
 Thanks for all the help @jorisvandenbossche !  It was my first contribution to a large open source project and I learned a lot, next time should be much smoother.
