PHP: fix string, number and folding region ; refactor styles
- new styles: Symbol, Operator, Scope Resolution, Error Control Operator, Cast, Heredoc, Nowdoc
- remove hard colors
- fix folding region of alternate block / ternary
- fix variable expansion in string and heredoc
- fix '_' in a number
- add missing keywords (yield from, parent, self, ...)
- add some functions / constants