DOC: some reviewing of the 0.20 whatsnew file
State: closed

Taking the opportunity to do some further edits to the whatsnew file

Labels:
name: Docs

Comments:
Mainly some rewording to make things a bit clearer (IMO), and some sphinx fixes.

I also added the warning about IntervalIndex being experimental that were in the main docs also in the whatsnew file
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16254?src=pr&el=h1) Report
> Merging [#16254](https://codecov.io/gh/pandas-dev/pandas/pull/16254?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/a31c96d34d00dc757908b564dc93991e867d83e2?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16254/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/16254?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16254      +/-   ##
==========================================
- Coverage   90.33%   90.33%   -0.01%     
==========================================
  Files         164      164              
  Lines       50890    50890              
==========================================
- Hits        45972    45969       -3     
- Misses       4918     4921       +3
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.11% <ø> (+0.01%)` | :arrow_up: |
| #single | `40.3% <ø> (-0.1%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16254?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/interval.py](https://codecov.io/gh/pandas-dev/pandas/pull/16254?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9pbnRlcnZhbC5weQ==) | `92.58% <ø> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/16254?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/16254?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.58% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/16254?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `91.03% <0%> (+0.34%)` | :arrow_up: |
| [pandas/\_version.py](https://codecov.io/gh/pandas-dev/pandas/pull/16254?src=pr&el=tree#diff-cGFuZGFzL192ZXJzaW9uLnB5) | `44.65% <0%> (+1.9%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16254?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/16254?src=pr&el=footer). Last update [a31c96d...91a330b](https://codecov.io/gh/pandas-dev/pandas/pull/16254?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/16254?src=pr&el=h1) Report
> Merging [#16254](https://codecov.io/gh/pandas-dev/pandas/pull/16254?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/a31c96d34d00dc757908b564dc93991e867d83e2?src=pr&el=desc) will **increase** coverage by `0.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16254/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/16254?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16254      +/-   ##
==========================================
+ Coverage   90.33%   90.35%   +0.01%     
==========================================
  Files         164      164              
  Lines       50890    50890              
==========================================
+ Hits        45972    45980       +8     
+ Misses       4918     4910       -8
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.13% <ø> (+0.03%)` | :arrow_up: |
| #single | `40.3% <ø> (-0.1%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16254?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/interval.py](https://codecov.io/gh/pandas-dev/pandas/pull/16254?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9pbnRlcnZhbC5weQ==) | `92.58% <ø> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/16254?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/16254?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.58% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/16254?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.23% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/16254?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `91.03% <0%> (+0.34%)` | :arrow_up: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/16254?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `65.05% <0%> (+1.81%)` | :arrow_up: |
| [pandas/\_version.py](https://codecov.io/gh/pandas-dev/pandas/pull/16254?src=pr&el=tree#diff-cGFuZGFzL192ZXJzaW9uLnB5) | `44.65% <0%> (+1.9%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16254?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/16254?src=pr&el=footer). Last update [a31c96d...91a330b](https://codecov.io/gh/pandas-dev/pandas/pull/16254?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).

@TomAugspurger added a commit with a few further updates. Can you take a quick look? (travis seems ok)