rolling.quantile returns an interpolated result
 - [x] closes #9413 
 - [x] tests added / passed
 - [x] passes ``git diff upstream/master --name-only -- '*.py' | flake8 --diff``
 - [x] whatsnew entry

add the examples as tests from #9413  # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16216?src=pr&el=h1) Report
> Merging [#16216](https://codecov.io/gh/pandas-dev/pandas/pull/16216?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/f1549668c84b481a67547bb46261d1394c8dd3e7?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/16216/graphs/tree.svg?height=150&width=650&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/16216?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #16216   +/-   ##
=======================================
  Coverage   90.89%   90.89%           
=======================================
  Files         162      162           
  Lines       50884    50884           
=======================================
  Hits        46250    46250           
  Misses       4634     4634
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.67% <ø> (ø)` | :arrow_up: |
| #single | `40.31% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16216?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/16216?src=pr&el=footer). Last update [f154966...ba5c751](https://codecov.io/gh/pandas-dev/pandas/pull/16216?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/16216?src=pr&el=h1) Report
> Merging [#16216](https://codecov.io/gh/pandas-dev/pandas/pull/16216?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/2002da33b0a755fcf7ef64b2c87ca4252f0e7df0?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/16216/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/16216?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16216      +/-   ##
==========================================
- Coverage   90.25%   90.23%   -0.02%     
==========================================
  Files         164      162       -2     
  Lines       50894    50882      -12     
==========================================
- Hits        45934    45914      -20     
- Misses       4960     4968       +8
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.02% <ø> (-0.01%)` | :arrow_down: |
| #single | `40.31% <ø> (-0.1%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16216?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/16216?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/conftest.py](https://codecov.io/gh/pandas-dev/pandas/pull/16216?src=pr&el=tree#diff-cGFuZGFzL2NvbmZ0ZXN0LnB5) | `95.45% <0%> (-0.38%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/16216?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.58% <0%> (-0.1%)` | :arrow_down: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/16216?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `78.78% <0%> (-0.09%)` | :arrow_down: |
| [pandas/io/clipboard/clipboards.py](https://codecov.io/gh/pandas-dev/pandas/pull/16216?src=pr&el=tree#diff-cGFuZGFzL2lvL2NsaXBib2FyZC9jbGlwYm9hcmRzLnB5) | | |
| [pandas/io/clipboard/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/16216?src=pr&el=tree#diff-cGFuZGFzL2lvL2NsaXBib2FyZC9fX2luaXRfXy5weQ==) | | |
| [pandas/util/\_decorators.py](https://codecov.io/gh/pandas-dev/pandas/pull/16216?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvX2RlY29yYXRvcnMucHk=) | | |
| [pandas/util/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/16216?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvX19pbml0X18ucHk=) | | |
| [pandas/util/\_validators.py](https://codecov.io/gh/pandas-dev/pandas/pull/16216?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvX3ZhbGlkYXRvcnMucHk=) | | |
| [pandas/io/clipboard/exceptions.py](https://codecov.io/gh/pandas-dev/pandas/pull/16216?src=pr&el=tree#diff-cGFuZGFzL2lvL2NsaXBib2FyZC9leGNlcHRpb25zLnB5) | | |
| ... and [22 more](https://codecov.io/gh/pandas-dev/pandas/pull/16216?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16216?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/16216?src=pr&el=footer). Last update [2002da3...1274fcc](https://codecov.io/gh/pandas-dev/pandas/pull/16216?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @jreback  I think that I have implemented all the requested improvements.

EDIT: Some tests failed in circleci, but ran OK in my machine. @jreback. Tests passed and changes implemented. @jreback I closed this a created a clean PR: #16247 pls don't open new pr's for the same issue, you simply push to the same PR. ok on this one.
 Sorry. Just trying to make things right. 