DOC: Docstring script to not require ending period for bullet points
- [X] closes #25461
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

This PR tries to solve the issue #25461 .

I thought that the validator should check that the last line of the parameter description is a part of a bullet point before raising the error PR09.

In order to do that, I had to add an extra method in the Docstring class that return a parameter description line by line (in a list). This is because Docstring.parameter_desc() returns the description as 1 string.

Please let me know how I can improve this or if I did not consider something.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25786?src=pr&el=h1) Report
> Merging [#25786](https://codecov.io/gh/pandas-dev/pandas/pull/25786?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/c975fc437744a62fffcc4a519cc124b025035f26?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/25786/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25786?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #25786      +/-   ##
==========================================
+ Coverage   91.26%   91.26%   +<.01%     
==========================================
  Files         172      172              
  Lines       52965    52965              
==========================================
+ Hits        48337    48338       +1     
+ Misses       4628     4627       -1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.82% <ø> (ø)` | :arrow_up: |
| #single | `41.74% <ø> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/25786?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/25786/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `89.44% <0%> (+0.09%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25786?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/25786?src=pr&el=footer). Last update [c975fc4...9bb2fa4](https://codecov.io/gh/pandas-dev/pandas/pull/25786?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/25786?src=pr&el=h1) Report
> Merging [#25786](https://codecov.io/gh/pandas-dev/pandas/pull/25786?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/f6a5dd4b8c450d73f3bec964b05cca32cef4bb71?src=pr&el=desc) will **decrease** coverage by `0.98%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/25786/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25786?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #25786      +/-   ##
==========================================
- Coverage   93.02%   92.04%   -0.99%     
==========================================
  Files         182      180       -2     
  Lines       50257    50713     +456     
==========================================
- Hits        46750    46677      -73     
- Misses       3507     4036     +529
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.68% <ø> (-1.01%)` | :arrow_down: |
| #single | `41.88% <ø> (-0.62%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/25786?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/25786/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `88.88% <0%> (-11.12%)` | :arrow_down: |
| [pandas/io/excel/\_openpyxl.py](https://codecov.io/gh/pandas-dev/pandas/pull/25786/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2V4Y2VsL19vcGVucHl4bC5weQ==) | `84.71% <0%> (-3.23%)` | :arrow_down: |
| [pandas/util/\_decorators.py](https://codecov.io/gh/pandas-dev/pandas/pull/25786/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvX2RlY29yYXRvcnMucHk=) | `92.13% <0%> (-3.22%)` | :arrow_down: |
| [pandas/core/dtypes/cast.py](https://codecov.io/gh/pandas-dev/pandas/pull/25786/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2Nhc3QucHk=) | `90.72% <0%> (-2.34%)` | :arrow_down: |
| [pandas/io/formats/printing.py](https://codecov.io/gh/pandas-dev/pandas/pull/25786/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvcHJpbnRpbmcucHk=) | `86.72% <0%> (-2.11%)` | :arrow_down: |
| [pandas/core/indexing.py](https://codecov.io/gh/pandas-dev/pandas/pull/25786/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhpbmcucHk=) | `93.48% <0%> (-1.55%)` | :arrow_down: |
| [pandas/core/dtypes/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/25786/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2NvbW1vbi5weQ==) | `96.35% <0%> (-1.44%)` | :arrow_down: |
| [pandas/core/arrays/categorical.py](https://codecov.io/gh/pandas-dev/pandas/pull/25786/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2NhdGVnb3JpY2FsLnB5) | `95.92% <0%> (-1.27%)` | :arrow_down: |
| [pandas/core/groupby/ops.py](https://codecov.io/gh/pandas-dev/pandas/pull/25786/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ3JvdXBieS9vcHMucHk=) | `96% <0%> (-0.92%)` | :arrow_down: |
| [pandas/core/internals/construction.py](https://codecov.io/gh/pandas-dev/pandas/pull/25786/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzL2NvbnN0cnVjdGlvbi5weQ==) | `95.95% <0%> (-0.84%)` | :arrow_down: |
| ... and [163 more](https://codecov.io/gh/pandas-dev/pandas/pull/25786/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25786?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/25786?src=pr&el=footer). Last update [f6a5dd4...43ae6ea](https://codecov.io/gh/pandas-dev/pandas/pull/25786?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Hello @EdAbati! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:





There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2019-10-24 22:25:43 UTC @EdAbati as mentioned if you can add tests will take a look Hi @WillAyd , sorry for the delay.

I just added a couple of tests.
Please let me know if and how I can improved this.

Thank you very much can you merge master Hi @WillAyd,
I was wondering if you had the chance to have a look at this,
Is there anything I should improve/change? Thanks for the ping and sorry forgot about this. I’m traveling the next two weeks but will try to fit another review round in then. 

Sent from my iPhone

> On Jun 18, 2019, at 5:47 PM, EdAbati <notifications@github.com> wrote:
> 
> Hi @WillAyd,
> I was wondering if you had the chance to have a look at this,
> Is there anything I should improve/change?
> 
> —
> You are receiving this because you were mentioned.
> Reply to this email directly, view it on GitHub, or mute the thread.
 @EdAbati can you rebase @EdAbati CI should be fixed now if you can merge master again. Hi @EdAbati I've been on vacation the past few weeks so haven't looked in detail. Back in a few days will review within the next week what is status here? The PR I mentioned has been merged already, you can open this PR in numpydoc now.