Add helpers for getting the line / column of a region

I couldn't find these built in for emacs. Weird.

Also, one of the tests (the one for the end column) fails for me on the
first try. The second try works. I don't have the energy to figure out
why. :|
Implement extracting a method from the currently selected text

Both emacs and evil mode selections should be supported now
Add "extract method" to README
Document the OmniSharpServer version on which this relies

This is the minimum version on the server side.
This should be updated whenever there is a change to omnisharp-emacs
that requires a newer version of OmniSharpServer.
Bump version 2.2 -> 2.3