* Add some missing Lua string syntax
All Lua strings have the string functions inside of them.
'...you can use the string functions in object-oriented style'
See '6.4 – String Manipulation' in https://www.lua.org/manual/5.3/manual.html
* Lua - Highlight self and TODO/NOTE/FIXME
* Add Lua 'arg' and triple-dot syntax
Use the 'regexp2' library for lookahead and lookbehind in region
start and end regular expressions to support things like closing quotes
that aren't preceded by backslashes.