Added toggling for abbreviations

-Created toggle function in global namespace
-Added initialization code with support for user-provided initial value
-Renamed NewUuid() to “namespace” the function to Nuuid
Fixed issue sourcing .vimrc with abbrevs turned off

-Added else statement to rerun unabbrev in case setting is disabled in
.vimrc
-Added silent to unabbrevs prevent unnecessary messages
-Removed I from abbrev toggle command name
Initial pass at markdown documentation