DEPR, DOC: Deprecate buffer_lines in read_csv
`buffer_lines` is not respected, as it is determined internally via a heuristic involving `table_width` (see <a href="https://github.com/pydata/pandas/blob/master/pandas/parser.pyx#L527">here</a> for how it is computed).

## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/13360?src=pr) is **84.23%**

> Merging [#13360](https://codecov.io/gh/pydata/pandas/pull/13360?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will increase coverage by **<.01%**

``` diff
@@             master     #13360   diff @@
==========================================
  Files           138        138          
  Lines         50724      50725     +1   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits          42726      42727     +1   
  Misses         7998       7998          
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last updated by [103f7d3...87eff55](https://codecov.io/gh/pydata/pandas/compare/103f7d31e1b850e532ed85a4b53ef222d1271c54...87eff55c436e01d15c82522aecbae053281ba24a)
 @jreback : Made the requested doc change, and Travis is giving the green light.  Ready to merge if there is nothing else.
 ty
