ENH: Series has gained the properties .is_monotonic*
## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/13336?src=pr) is **84.23%**

> Merging [#13336](https://codecov.io/gh/pydata/pandas/pull/13336?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will increase coverage by **<.01%**

``` diff
@@             master     #13336   diff @@
==========================================
  Files           138        138          
  Lines         50703      50710     +7   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits          42705      42712     +7   
  Misses         7998       7998          
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last updated by [f3d7c18...0a50ff9](https://codecov.io/gh/pydata/pandas/compare/f3d7c18190045bdf02f4448e46880a7030829716...0a50ff924d8ba97a09aeda52d6318e89ffa53862)
