Turns out I don't need this to resolve CoreText optical sizing
issue after all.

https://github.com/behdad/harfbuzz/issues/360

This one:

  map->mask = (1 << (next_bit + bits_needed)) - (1 << next_bit);

before the fix, the shift was done as an int, causing overflow
if it ever got to 1 << 31.  Sprinkle 'u's around.

Fixes https://bugs.chromium.org/p/chromium/issues/detail?id=634805

A while back we marked every API as version:1.0.  We should fix them all
to reflect real version they were introduced.  This is a start.

Patch from Nikolay Sivov.

Based on data from http://upstream-tracker.org/versions/harfbuzz.html
Resolves #103

Previously, when creating an object from inert inputs (eg:
"hb_font_create(hb_face_get_empty())") we returned the inert
empty object.  This is not helpful as there are legitimate
usecases to do that.

We now never return the inert object unless allocation failed.

Tests are revised to reflect.

Ouch!

Should move these out of the public header...

We're "clean" of introspection warnings now.  Remaining ones are about
graphite2 / freetype types not being introspectable.

Since our types are not associated with their methods, marking
constructors makes them inaccessible from bindings.  Undo for now.

Makes documentation / introspection easier.