Implement functions for region and coordinate handling into sublime_lib
Implement functions for region and coordinate handling into sublime_lib

These are pretty useful when you want to extract a specific part of the
buffer (like line 1 or the two last lines) and also checks the coordinates
for validity unlike ``view.text_point()``
(try ``print view.rowcol(view.text_point(0, 100000))`` and you'll see).

SublimeText/AAAPackageDev,SublimeText/AAAPackageDev,SublimeText/PackageDev