Ran 2to3.py on python files to upgrade to v3
Rewritten method to add sublime_lib to system path

In sublime Text 3 calls to sublime methods are restricted during
startup. Full path to sublime_lib must therefore only use system calls.
Use path relative to AAA.py.
Make import mock work in Python 3
Replace usage of begin_edit/end_edit

begin_edit/end_edit are restricted in Sublim Text 3. Use class derived
from TextCommand to get hold of the edit object.