Now that we use C++ for all source code, lets benefit from it!

The hb_be_int16/32_get/put/eq() macros grow code size if replaced with
inline functions, so leave them as is.

Would have been nice if gcc had warned...

Makes way for adding arbitrary user_data support.

Unused right now.

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

It's just sugar.

Since we now assert thos in hb-private.h, the int types cannot be wrong.
(Except for when someone else includes hb-common.h in a very broken
configuration, but that's not our problem!)

Plus, we don't use inline in the public headers, so remove that too.

__LOC__ was renamed to _HB__LOC__ in cd7555 but the corresponding
change wasn't made in hb-private.h.

Kinda hand-wavy right now.  Not tested.

hb_font_set_scale() now sets the value to be used to represent a unit
pixel.  For example, if rendering a 10px font with a 26.6 representation,
you would set scale to (10 << 6).  For 10px in 16.16 you would set it to
(10 << 16).  This space should be the same space that the get_glyph_metrics
and get_kerning callbacks work in.

So we can apply it to class methods also.  Not sure if that works!

Shrinks .text by 1%!

Also remove wrong ASSERT_SIZE that would trigger only when not using
flexible arrays (which was the case on win32, but not with gcc).