Make --font-file accept "-" to mean stdin, and have it work
in Windows too!

Apparently there's no equivalent to "/dev/stdout", so write using
stdio to be able to output to stdout.

Now we can use the same code to do other utils...

We now support using -1 for NUL-terminated strings.

Can be -1 for NUL-terminated string.  This is useful for passing parts
of a larger string to a function without having to copy or modify the
string first.

Affected functions:

	hb_tag_t hb_tag_from_string()
	hb_direction_from_string()
	hb_language_from_string()
	hb_script_from_string()

For two reasons:

1. User can always call hb_buffer_pre_allocate() themselves, and

2. Now we do a pre_alloc in add_utfX anyway, so the total number of
reallocs is limited to a small number (~3) anyway.  This just makes the
API cleaner.

Using graphite2's comparerenderer suggests that this makes hb-ft 15
times faster.  No caching layer needed anymore.

If the specified shapers fail, hb-shape will fail immediately