Added support for command line arguments to be passed in directly, or
to use builtin defaults if only the filename is passed in.

Currently, this is hardwired to ac-clang-cflags
Fixed mega bug where an idle timer calls clang-faces-request-hilight
but the current buffer (that created the timer) isn't set when woken
from an idle timer!

This was causing massive refontify's of the entire buffer and flooding
the queue for the active buffer (not to mention the chaos that
happened when the active buffer wasn't a C source file)