DOC: Clean-up references to v12 to v14 (both included)
- [ ] closes #xxxx
- [ ] tests added / passed
- [x ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

This is a continution of #17375 and cleans up references to old versions of pandas in the documentation.

Somme issues, I'd appreciate input on:
* In ``enhancingperf.rst`` there is under "Expression Evaluation via :func:`~pandas.eval` (Experimental)" and "The ``DataFrame.eval`` method (Experimental)" a line ``..versionadded:: 0.13``.
  In general I think it's a bit weird that something introduced back in 0.13 still is marked as experimental. I've let the versionadded stay for now, to somehow mark that ``eval`` is quite old even though it is experimental. Are there thoughts whether ``eval`` should still be marked experimental?
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17420?src=pr&el=h1) Report
> Merging [#17420](https://codecov.io/gh/pandas-dev/pandas/pull/17420?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/1981b679b0619de0765c2009684ce4abd886189d?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17420/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/17420?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17420      +/-   ##
==========================================
- Coverage   91.15%   91.14%   -0.02%     
==========================================
  Files         163      163              
  Lines       49581    49581              
==========================================
- Hits        45198    45190       -8     
- Misses       4383     4391       +8
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.92% <ø> (ø)` | :arrow_up: |
| #single | `40.25% <ø> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17420?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/17420?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17420?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.72% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/17420?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.43% <0%> (+0.09%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17420?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/17420?src=pr&el=footer). Last update [1981b67...aee6a29](https://codecov.io/gh/pandas-dev/pandas/pull/17420?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/17420?src=pr&el=h1) Report
> Merging [#17420](https://codecov.io/gh/pandas-dev/pandas/pull/17420?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/1981b679b0619de0765c2009684ce4abd886189d?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17420/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/17420?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17420      +/-   ##
==========================================
- Coverage   91.15%   91.14%   -0.02%     
==========================================
  Files         163      163              
  Lines       49581    49581              
==========================================
- Hits        45198    45189       -9     
- Misses       4383     4392       +9
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.92% <ø> (ø)` | :arrow_up: |
| #single | `40.25% <ø> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17420?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/17420?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17420?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.72% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17420?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/17420?src=pr&el=footer). Last update [1981b67...b3d1ea1](https://codecov.io/gh/pandas-dev/pandas/pull/17420?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 > In enhancingperf.rst there is under "Expression Evaluation via :func:~pandas.eval (Experimental)" and "The DataFrame.eval method (Experimental)" a line ..versionadded:: 0.13.
In general I think it's a bit weird that something introduced back in 0.13 still is marked as experimental. I've let the versionadded stay for now, to somehow mark that eval is quite old even though it is experimental. Are there thoughts whether eval should still be marked experimental?

yeah you can take the Experimental off. ping @jreback  thanks!