Backport features and fixes from ST3 branch

-No longer use Sublime API regex. RegReplace now uses re everywhere for
consistency
-Properly adjust selections on selection regex
-Treat selections as their own buffer unless
"regex_full_file_with_selections" is set to "true"
-Allow fold and unfold in "on_save_sequence" via '"action": "fold"' or
'"action": "unfold"'
-deprecate '"highlight": true' in favor of '"action": "mark"'