Emacs: fix fontification of numbers and bytes constants
This fixes a small bug in the regular expressions for constant fontification in the Emacs Michelson mode: negative numbers and bytes literals were not supported. Since the result of fontification is used for indentation, this caused indentation issues when these unsupported constants appeared as part of sequences. I have attached a file that shows the problem: the file is well-indented and well-typed according to mockup_client typecheck script but without the patch Emacs reindents it badly.