Don't include skipped glyphs in combined bitmaps

Make sure to correctly handle situations where glyphs
have info->linebreak and info->skip set at the same time.

Fixes libass#44.
Added license headers in ASM files
Use lower mm registers in be_blur.asm
Added XMM register count in be_blur; should help #48
Remove unnecessary instruction
Fix limits.h includes

These were missing in several places. Fixes #50.
Define HAVE_ALIGNED_STACK; should wrap up #48
We have aligned stack on Win64
Update changelog
Update version info
Update changelog
Add missing distfiles
Update version info and changelog
Create README.md
Format README.md
Redesigned configure/Makefile setup

Adds yasm version check and handles Free/OpenBSD/win32 correctly.

Signed-off-by: Grigori Goronzy <greg@chown.ath.cx>
Assume SSE2 on x86_64
Don't use an unsigned it to check for <0 :|
Don't crash on \fscx0

Freetype can return a bounding box with all fields set to INT_MIN if an
outline with all points set to 0 is used. This can happen e.g. with
\fscx0, but also in more complicated cases. (In the original crashing
sample, this was probably caused in combination with an embedded font.)

Such a bounding box causes libass to crash, because it will enlarge the
combined bitmap bounding box to a ridiculous size.

Just skip outlines that have en empty bounding box. This is probably
the correct thing to do, and won't pass INT_MAX down to other parts
of libass.
Actually export ass_library_version symbol

Patch by chadr...@gmail.com.

Fixes libass#58, GC#117.