Multi-bugfix invoking cmdline args.

Commandline args weren't actually be using! Fixed and correctly
invoking the process with these args using `apply' now.
Renamed executable to clang-faces and renamed executable elisp var to
`clang-faces-exec'
Idle timer functionality changed - if the buffer's modified tick
hasn't changed since the previous hilight request, we return without
making a new hilight request.

Now idle buffers should re-hilight just once and then go silent.