We need to know whether the glyph exists, so we can fallback to
composing / decomposing.  Assuming that glyph==0 means "doesn't exist"
wouldn't work for applications like Pango that want to use different
"doesn't exist" glyph codes for different characters.  An explicit
return value fixes that.

Makes it clear that kerning is in visual order.

Test passing now.

get_contour_point now takes glyph id before point_index.

get_kerning now takes a vector to fill-in.

Not quite useful just yet.

Mutex (and Windows.h by extension) are fairly isolated now.

Needed to be able to include <Windows.h> from hb-object-private.h.

Will be adding font_funcs subclassing instead.

Makes way for adding arbitrary user_data support.

I was reconsidering whether y should grow down, since all three/four
times I've used this API I was tricked and got that wrong in my use.
So I was very inclined to make y grow down instead of up.  However,
considering that the font space has y up and it would be very confusing
for callbacks to work against that, I decided that what I really want
is for the user to be able to set y_scale to a negative number to imply
that user-space y grows down.

Changing x_scale/y_scale from unsigned int to int allows that, and I've
made pango to use that instead of negating glyph y_offset later.  hb-ft
however still has y group up.  I *guess* that's how FreeType works?
I'm not sure, FreeType docs don't make this clear...

I'm happy with the resolution :-).

So we can liberally use the simple features of C++ that parts of the
codebase is already using.

The idea here is that:

  - Like pretty much all other API in harfbuzz, user does not have to
    check for NULL.

  - In any caller code, the case of missing table should be handled
    exactly the same way that a too-short table is handled.  Turning
    a non-existent talbe into a table of size 0 makes the user code
    safer.

That correctly reflects the reference ownership transfer happening.

This was a bizzare piece of API that I inherited from cairo.  It has
been wrong adding them to cairo in the first place.  Remove them before
someone uses them!

This is the common convention for language binding tools.

Graphite module not updated.
Bump version to 0.3.

Correspond to the make_mutable() ones.