DOC: Correct/update skipna docstrings for `any` and `all` (#23109)
Also, include examples with NA values and describe treatment of NA with `skipna == False`

- [x] closes #23109
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Hello @jamesmyatt! Thanks for updating the PR.

 - There are no PEP8 issues in the file [`pandas/core/generic.py`](https://github.com/jamesmyatt/pandas/blob/32821431d56a5222be149ece45faa8f76361a5da/pandas/core/generic.py) !



##### Comment last updated on December 10, 2018 at 14:45 Hours UTC # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24069?src=pr&el=h1) Report
> Merging [#24069](https://codecov.io/gh/pandas-dev/pandas/pull/24069?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/a7bb9720e969e1bb09165a2e3828b8ef70914196?src=pr&el=desc) will **increase** coverage by `49.86%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24069/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24069?src=pr&el=tree)

```diff
@@             Coverage Diff             @@
##           master   #24069       +/-   ##
===========================================
+ Coverage   42.38%   92.25%   +49.86%     
===========================================
  Files         161      161               
  Lines       51699    51699               
===========================================
+ Hits        21913    47694    +25781     
+ Misses      29786     4005    -25781
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.65% <100%> (?)` | |
| #single | `42.38% <40%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24069?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/24069/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `96.65% <100%> (+57.31%)` | :arrow_up: |
| [pandas/core/computation/pytables.py](https://codecov.io/gh/pandas-dev/pandas/pull/24069/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tcHV0YXRpb24vcHl0YWJsZXMucHk=) | `92.37% <0%> (+0.3%)` | :arrow_up: |
| [pandas/io/pytables.py](https://codecov.io/gh/pandas-dev/pandas/pull/24069/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3B5dGFibGVzLnB5) | `92.3% <0%> (+0.92%)` | :arrow_up: |
| [pandas/util/\_test\_decorators.py](https://codecov.io/gh/pandas-dev/pandas/pull/24069/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvX3Rlc3RfZGVjb3JhdG9ycy5weQ==) | `93.24% <0%> (+4.05%)` | :arrow_up: |
| [pandas/compat/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/24069/diff?src=pr&el=tree#diff-cGFuZGFzL2NvbXBhdC9fX2luaXRfXy5weQ==) | `58.36% <0%> (+8.17%)` | :arrow_up: |
| [pandas/core/config\_init.py](https://codecov.io/gh/pandas-dev/pandas/pull/24069/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29uZmlnX2luaXQucHk=) | `99.24% <0%> (+9.84%)` | :arrow_up: |
| [pandas/core/reshape/util.py](https://codecov.io/gh/pandas-dev/pandas/pull/24069/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS91dGlsLnB5) | `100% <0%> (+11.53%)` | :arrow_up: |
| [pandas/compat/numpy/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/24069/diff?src=pr&el=tree#diff-cGFuZGFzL2NvbXBhdC9udW1weS9fX2luaXRfXy5weQ==) | `92.85% <0%> (+14.28%)` | :arrow_up: |
| [pandas/core/computation/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/24069/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tcHV0YXRpb24vY29tbW9uLnB5) | `85.71% <0%> (+14.28%)` | :arrow_up: |
| [pandas/core/api.py](https://codecov.io/gh/pandas-dev/pandas/pull/24069/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXBpLnB5) | `100% <0%> (+14.81%)` | :arrow_up: |
| ... and [120 more](https://codecov.io/gh/pandas-dev/pandas/pull/24069/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24069?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/24069?src=pr&el=footer). Last update [a7bb972...df91bcb](https://codecov.io/gh/pandas-dev/pandas/pull/24069?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24069?src=pr&el=h1) Report
> Merging [#24069](https://codecov.io/gh/pandas-dev/pandas/pull/24069?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/0ac1197c0597d2d55b1ebf0a245c31bc1fa38e19?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/24069/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24069?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #24069      +/-   ##
==========================================
+ Coverage   92.21%   92.21%   +<.01%     
==========================================
  Files         162      162              
  Lines       51721    51723       +2     
==========================================
+ Hits        47692    47694       +2     
  Misses       4029     4029
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.61% <100%> (-0.01%)` | :arrow_down: |
| #single | `43.03% <100%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24069?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/24069/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `96.65% <100%> (ø)` | :arrow_up: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/24069/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `96.91% <0%> (ø)` | :arrow_up: |
| [pandas/core/arrays/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/24069/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2RhdGV0aW1lcy5weQ==) | `98.56% <0%> (ø)` | :arrow_up: |
| [pandas/io/pytables.py](https://codecov.io/gh/pandas-dev/pandas/pull/24069/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3B5dGFibGVzLnB5) | `92.31% <0%> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24069?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/24069?src=pr&el=footer). Last update [0ac1197...3282143](https://codecov.io/gh/pandas-dev/pandas/pull/24069?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 pls also merge master. ping on green. can you also merge master @jreback , will do as soon as I've made the outstanding changes.

Do you have any views on the comments above? @jamesmyatt, added a comment (sorry for the delay), let me know if you need any other information to finish this PR @jreback , @datapythonista , I think this should be ready now. Thanks. Thanks, @datapythonista . 

I haven't been able to run validate_docstrings.py because I can't build pandas yet: I'm using Windows and I installed the C compiler yet. Although, I have checked the new examples manually: https://gist.github.com/jamesmyatt/8c6aa9178346e25e3175500672714ca5

BTW, it's a bit annoying that the [contributing guide](https://pandas.pydata.org/pandas-docs/stable/contributing.html) linked from README doesn't match what's in master: I had lots of trouble with the environment files for a little while. The contributing guide you are using is for `stable`, which means `0.23.4`. 

The one corresponding to `master` is the one in the devs docs: https://pandas-docs.github.io/pandas-docs-travis/contributing.html

It could make sense to somehow "hide" the one for master, and have a link for the devs, as it's probably the only relevant one. How to do this is probably not trivial. But creating an issue, and may be a PR if you have an idea on how to address that, would be useful. I've run `./scripts/validate_docstrings.py pandas.Series.any` and `all` now and fixed the errors.

Turns out it's not so hard to install the compiler for Windows these days. I'll suggest an improvement to contributing.rst later. thanks. ping on green. @jreback , ping.

There are 2 warnings in PublishTestResults, which I assume is nothing to do with this. thanks!