DOC: Correct docstring formatting for excel related functions GH23494
- [X] closes #23494 
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Addresses failed validations from validate_docstrings.py in pandas.read_excel

First open source pull request! Looking to improve.
Hello @timdef! Thanks for updating the PR.

 - In the file [`pandas/io/excel.py`](https://github.com/timdef/pandas/blob/a0a3f991080924d68a9e51256379c8dfceac08bb/pandas/io/excel.py), following                are the PEP8 issues :
> [Line 200:80](https://github.com/timdef/pandas/blob/a0a3f991080924d68a9e51256379c8dfceac08bb/pandas/io/excel.py#L200): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (83 > 79 characters)




##### Comment last updated on November 06, 2018 at 14:58 Hours UTC Two things that the validation called out that I wasn't certain about:
1. Sometimes the parameter description ends with a bulleted list, validation would like a '.' on the last item of that list, even if the other items don't end in periods.
2. Deprecated parameters often don't currently have descriptions, only deprecated warnings. I had to put above warning to get validation to pass. Is this desired? Also, still currently have these errors:
```
3 Errors found:
	Errors in parameters section
		Parameters {**kwds, date_parser, parse_dates} not documented
		Unknown parameters {parse_cols, sheetname, skip_footer, keep_default_na, verbose}
2 Warnings found:
	No extended summary found
	See Also section not found
```

Wanted to see if I should take a stab at correcting these or if this work was more about bringing things in line format-wise with the validator. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23505?src=pr&el=h1) Report
> Merging [#23505](https://codecov.io/gh/pandas-dev/pandas/pull/23505?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/0bb24b7ac5c58bf9115485bba8c8b97442ab5059?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/23505/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23505?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #23505   +/-   ##
=======================================
  Coverage   92.23%   92.23%           
=======================================
  Files         161      161           
  Lines       51197    51197           
=======================================
  Hits        47220    47220           
  Misses       3977     3977
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.61% <ø> (ø)` | :arrow_up: |
| #single | `42.27% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23505?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/23505?src=pr&el=footer). Last update [0bb24b7...a0a3f99](https://codecov.io/gh/pandas-dev/pandas/pull/23505?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 > Wanted to see if I should take a stab at correcting these or if this work was more about bringing things in line format-wise with the validator.

@timdef : First off, congrats on your first PR!  I think it would be a good idea to attempt to patch these. can you merge master, ``pandas.io.excel`` was refactored a bit @timdef do you have time to address the comments and fix the conflicts? closing as stale. if you'd like to continue working, pls ping.