Improve Python 2.7 inspect stub
Improve Python 2.7 inspect stub

This patch consists of:

* Splitting and reordering the content into sections corresponding
  to the module's documentation sections
* Implementing some missing functions
* Adding TODOs for missing stuff (I may've missed something)

The signature of isgenerator() (was: Any argument, is: argument of type
object) is changed for consistency with other is* functions I added
here, after some considerations I couldn't decide whether it should be
object or Any - if object is not advised please let me know.

azag0/typeshed,fyquah95/typeshed,tharvik/typeshed,li-dan/typeshed,tharvik/typeshed,fyquah95/typeshed,euresti/typeshed