Usage of 'limit' keyword when filling with a value
From SO: http://stackoverflow.com/questions/29906512/pandas-variation-on-filling-nan-whats-an-elegant-and-pythonic-way-to-do-thi/29906743?noredirect=1#29906743

When doing `df.fillna(10, limit=2)` what is `limit=2` doing?

The [docstring](http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.fillna.html) says:

> limit : int, default None
>               Maximum size gap to forward or backward fill

But this only explains for filling with a method, not for filling with a value.
