CLI improvements

[Lyrth]

Some suggestions for Clue's command-line interface

• [x] - flag in place of the filename to read Clue script from stdin (moved from #132)
• [ ] --quiet, -q flag to suppress info messages from output; warnings and errors should both be piped to stderr (see above linked issue)
• [ ] Compiler flag for LL/ULL handling on non-LuaJIT targets, maybe accepts none, remove, warn, error.
• [ ] Treat --target as preset set of options that can be overridden by individual compiler flags. May have to expose more flags for the other settings that each target changes.