BUG: Accept dict or Series in fillna for categorical Series
- [ ] closes #17033
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Hello @reidy-p! Thanks for updating the PR.











Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on November 20, 2017 at 20:06 Hours UTC # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18293?src=pr&el=h1) Report
> Merging [#18293](https://codecov.io/gh/pandas-dev/pandas/pull/18293?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/8d04dafd48d541042613548183b62288ef7e97b3?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `94.11%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18293/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/18293?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18293      +/-   ##
==========================================
- Coverage   91.36%   91.34%   -0.02%     
==========================================
  Files         164      164              
  Lines       49721    49729       +8     
==========================================
- Hits        45429    45427       -2     
- Misses       4292     4302      +10
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.14% <94.11%> (-0.01%)` | :arrow_down: |
| #single | `39.6% <0%> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18293?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/18293?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `95.73% <100%> (ø)` | :arrow_up: |
| [pandas/core/categorical.py](https://codecov.io/gh/pandas-dev/pandas/pull/18293?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY2F0ZWdvcmljYWwucHk=) | `95.66% <93.75%> (-0.09%)` | :arrow_down: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18293?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18293?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.8% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18293?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/18293?src=pr&el=footer). Last update [8d04daf...c484f49](https://codecov.io/gh/pandas-dev/pandas/pull/18293?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 pls rebase as well (generally anytime you are pushing you should) thanks @reidy-p 