lua-font-lock-keywords: fontify constants/builtins first

Move constant/builtin fontification rules to the beginning so that they
have more priority than regular rules and can only be explicitly
overridden.
Add helper functions for reimplementation of font-lock-keywords
Major refactoring of font-lock-keywords:

- add highlighting of local var assignments with multiple variables
  local x,y,z = ...

- simple on-fly syntax check in local var assignments
  local 00xyz, foo, bar,, baz bux = ....
        ^^              ^     ^^^
        these are syntax errors and will be highlighted

- faster and more precise function name matching

- fix docstring; it was inside (eval-when-compile ...) block and hence
  considered one of the font-lock rules :)
Add var name highlighting in "for x,y in ..." construct
Improve local var assignment matching

- make sure == is a syntax error
- make sure names are matched on symbol boundaries
Add field containing commit SHA expanded during archive creation.
Bump copyright information (no luck with FSF), rephrase comment
Wrap symbols required during compilation into (eval-when compile ...)

lua-local-defun-regexp & lua-make-delimited-matcher are needed for
lua-font-lock-keywords initialization.