Also remove shaper_options argument to hb_shape_full().  That was
unused and for "future".  Let it go.

More shaper API coming in preparation for plan/planned API.

We need this to set data on objects safely without worrying that some
other thread unsets it by setting it at the same time.

hb_face_get_blob() renamed to hb_face_reference_blob(), returns a
reference now.

hb_face_[sg]et_index() added.

hb_face_set_upem() added.

It's kinda working finally!

Oops!

Not tested yet.

hb_shape() now accepts a shaper_options and a shaper_list argument.
Both can be set to NULL to emulate previous API.  And in most situations
they are expected to be set to NULL.

hb_shape() also returns a boolean for now.  If shaper_list is NULL, the
return value can be ignored.

shaper_options is ignored for now, but otherwise it should be a
NULL-terminated list of strings.

shaper_list is a NULL-terminated list of strings.  Currently recognized
strings are "ot" for native OpenType Layout implementation, "uniscribe"
for the Uniscribe backend, and "fallback" for the non-complex backend
(that will be implemented shortly).  The fallback backend never fails.

The env var HB_SHAPER_LIST is also parsed and honored.  It's a
colon-separated list of shaper names.  The fallback shaper is invoked if
none of the env-listed shapers succeed.

New API hb_buffer_guess_properties() added.

Where causing issues for people with MSVC.

Not complete yet, font selection doesn't work.  But hey it shapes!

This is not supposed to be a production backend, more like a testing
backend.