Resampler.__iter__() not working
- [x] closes #15314
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

dunder methods like __iter__ are included in the docs.

Although,
http://pandas-docs.github.io/pandas-docs-travis/generated/pandas.core.groupby.GroupBy.__iter__.html
isn't that great of a docstring at the moment :)

On Wed, Aug 15, 2018 at 10:25 AM Alex Rychyk <notifications@github.com>
wrote:

> *@discort* commented on this pull request.
> ------------------------------
>
> In pandas/core/resample.py
> <https://github.com/pandas-dev/pandas/pull/22365#discussion_r210306460>:
>
> > @@ -97,6 +97,18 @@ def __getattr__(self, attr):
>
>          return object.__getattribute__(self, attr)
>
> +    def __iter__(self):
> +        """
> +        Resampler iterator
> +
> +        Returns
> +        -------
> +        Generator yielding sequence of (name, subsetted object)
> +        for each group
> +        """
>
> @TomAugspurger <https://github.com/TomAugspurger>
>
> I wanted to make sure that we are on the same page. Should I add See Also
> section for a magic method __iter__? But it's an internal method, isn't
> it?
>
> —
> You are receiving this because you were mentioned.
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>
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22365?src=pr&el=h1) Report
> Merging [#22365](https://codecov.io/gh/pandas-dev/pandas/pull/22365?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/84af863c38d305db96403f0afc5fa73b98052d0e?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/22365/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/22365?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #22365      +/-   ##
==========================================
- Coverage   92.05%   92.05%   -0.01%     
==========================================
  Files         169      169              
  Lines       50709    50712       +3     
==========================================
+ Hits        46679    46681       +2     
- Misses       4030     4031       +1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.45% <100%> (-0.01%)` | :arrow_down: |
| #single | `42.25% <33.33%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/22365?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/resample.py](https://codecov.io/gh/pandas-dev/pandas/pull/22365/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzYW1wbGUucHk=) | `96.1% <100%> (+0.02%)` | :arrow_up: |
| [pandas/util/\_depr\_module.py](https://codecov.io/gh/pandas-dev/pandas/pull/22365/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvX2RlcHJfbW9kdWxlLnB5) | `65.11% <0%> (-2.33%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22365?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/22365?src=pr&el=footer). Last update [84af863...475c74d](https://codecov.io/gh/pandas-dev/pandas/pull/22365?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @jreback  thanks @discort 