Use FT_Outline_EmboldenXY if available
Remove bitmap restriding

It turns out we don't need this.
Fix change detection when text is clipped to screen

The glyphs are clipped before combining, so the combined bitmap can
always have the same position, size, and address. This breaks the
change detection. Or at least I think that's what happens.
Add BorderStyle=4, background color for text

This is somewhat similar to BorderStyle=3, but with a number of
differences. Mainly, this new BorderStyle doesn't create overlaps
within an event.

Closes #105.
Merge pull request #100 from astiob/stroke

Use FT_Outline_EmboldenXY
unistd.h is not needed
Move ASS_Shaper declaration to ass_shaper.h
Explicitly include ass_utils.h everywhere (and not config.h)
Fully fix compilation with MSVC/ICL

As before, this does not add any build system support:
a config.h file and a project must still be manually created
(or the compiler can be run manually instead of using a project).