COMPAT: alias .to_numpy() for scalars
``Timestamp`` and ``Timedelta`` scalars now implement `to_numpy()` as aliases to `Timestamp.to_datetime64` and `Timedelta.to_timedelta64`, respectively.

- [x] closes #24653
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Hello @cbertinato! Thanks for updating the PR.







Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on February 16, 2019 at 13:58 Hours UTC # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25142?src=pr&el=h1) Report
> Merging [#25142](https://codecov.io/gh/pandas-dev/pandas/pull/25142?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/2e38d5552a5c7b2c0091cecddd483f4f08ad1d2c?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/25142/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25142?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #25142   +/-   ##
=======================================
  Coverage   92.37%   92.37%           
=======================================
  Files         166      166           
  Lines       52408    52408           
=======================================
  Hits        48412    48412           
  Misses       3996     3996
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.79% <ø> (ø)` | :arrow_up: |
| #single | `42.86% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25142?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/25142?src=pr&el=footer). Last update [2e38d55...b98f7ed](https://codecov.io/gh/pandas-dev/pandas/pull/25142?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/25142?src=pr&el=h1) Report
> Merging [#25142](https://codecov.io/gh/pandas-dev/pandas/pull/25142?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/83fe6ca422ecc35f311897abedadcc492b2a0777?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/25142/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25142?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #25142   +/-   ##
=======================================
  Coverage   91.72%   91.72%           
=======================================
  Files         173      173           
  Lines       52831    52831           
=======================================
  Hits        48457    48457           
  Misses       4374     4374
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.28% <ø> (ø)` | :arrow_up: |
| #single | `41.72% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25142?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/25142?src=pr&el=footer). Last update [83fe6ca...c1ffa8f](https://codecov.io/gh/pandas-dev/pandas/pull/25142?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 All looks to be green now. Had to change the test for NaT to use `pd.isnull` because NumPy 1.12 doesn't have `isnat`. thanks @cbertinato nice!