changed descriptions

There's no moonscript in this project anymore.
libass link in markdown will be used just once, so can be inline.
updated Makefile for static library & windows
changed function names lowercase

Language is C, so definitions are full uppercase, structures can be partwise uppercase, but functions are lowercase only.
hide ASSI_State structure from users

Users shouldn't mess up anything, so just library functions work with a state.
(Library becomes object-oriented)
Additionally removes double include of libass.
added windows dll export
added version to preprocessor

Informations for users, like exported functions or version, belong to headers.
This makes access faster and often changed data easier to find.
improved performance of dirty pixels detection

For x64 compilers compares 8 bytes at once now, so taking advantage of bigger register sizes.
improved memory safety

Initializes relevant variables, checks allocations and avoids memory leaks.