Implement get_day_of_year, tests
Separates the ccalendar.get_day_of_year part out of #18540, implements tests, uses it in `Timestamp` renders Timestamp._get_field unnecessary.
Hello @jbrockmendel! Thanks for updating the PR.







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

##### Comment last updated on February 07, 2018 at 00:34 Hours UTC # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19555?src=pr&el=h1) Report
> Merging [#19555](https://codecov.io/gh/pandas-dev/pandas/pull/19555?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/93c86aa13e1b7816c762b4ff372aef80a7830af8?src=pr&el=desc) will **increase** coverage by `0.02%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/19555/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&height=150&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/19555?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #19555      +/-   ##
==========================================
+ Coverage    91.6%   91.63%   +0.02%     
==========================================
  Files         150      150              
  Lines       48750    48750              
==========================================
+ Hits        44657    44670      +13     
+ Misses       4093     4080      -13
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90% <100%> (+0.02%)` | :arrow_up: |
| #single | `41.75% <0%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/19555?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/19555/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.25% <100%> (ø)` | :arrow_up: |
| [pandas/io/parsers.py](https://codecov.io/gh/pandas-dev/pandas/pull/19555/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3BhcnNlcnMucHk=) | `95.56% <0%> (+0.06%)` | :arrow_up: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/19555/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `66.95% <0%> (+1.73%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19555?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/19555?src=pr&el=footer). Last update [93c86aa...5b11a2a](https://codecov.io/gh/pandas-dev/pandas/pull/19555?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 ok! love things that consolidate utilities