spearmint: Skip data after shader directive until brace or end of line

This allows adding new aruments to existing directives in the future without breaking parsing with past Spearmint versions (starting now).

Each directive should be on a separate line. Q3 will allow 'detail map path/to/image', Spearmint will skip after detail until end of line or finds a brace.

Note: q3map2 skips unknown general directives (q3/spearmint does not) and rest of line for known general directives. q3map2 does not skip rest of line in stage directives though.