ENH: Add divmod to series.
- [x] closes #8174
- [x] tests added / passed
- [x] passes `git diff upstream/master | flake8 --diff`
- [x] whatsnew entry

edit: in the issue it said this is uncommon; however, I recently ran into an issue where I was doing arithmetic with fiscal quarters and using divmod seemed more natural.

## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/14208?src=pr) is 85.24% (diff: 100%)

> Merging [#14208](https://codecov.io/gh/pydata/pandas/pull/14208?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will increase coverage by **<.01%**

``` diff
@@             master     #14208   diff @@
==========================================
  Files           140        140          
  Lines         50559      50567     +8   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits          43099      43107     +8   
  Misses         7460       7460          
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [5e2f9da...08b3939](https://codecov.io/gh/pydata/pandas/compare/5e2f9da6e8e713bd89cfe8760e63583ea7d29879...08b39390a0984748dcc08bfd83c3f45b7b43f554?src=pr)
 I moved this into `add_special_arithmetic_methods`
 I added `divmod` to  indices and made it less special for series. I don't see a simple way to get `divmod` on dataframe right now though.
 ping
 The clang build seemed to hang here, can we rerun it?
 Thank you for rerunning, looks to be passing now
 ping
 thanks @llllllllll 
 Thank you!
