Add Vim syntax highlighting for GLSL.

[brobeson]

Item	Implemented	Tested
preprocessor	:white_check_mark:	:white_check_mark:
define/undef	:white_check_mark:	:white_check_mark:
if/ifdef/ifndef/else/elif/endif	:white_check_mark:	:white_check_mark:
error	:white_check_mark:	:white_check_mark:
pragma	:white_check_mark:	:white_check_mark:
extension	:white_check_mark:	:white_check_mark:
version	:white_check_mark:	:white_check_mark:
line	:white_check_mark:	:white_check_mark:
types	:white_check_mark:	:white_check_mark:
qualifiers	:white_check_mark:	:white_check_mark:
image formats	:white_check_mark:	:white_check_mark:
built in variables	:white_check_mark:	:white_check_mark:
built in constants	:white_check_mark:	:white_check_mark:
built in macros	:white_check_mark:	:white_check_mark:
built in functions	:white_check_mark:	:white_check_mark:
errors	:white_check_mark:	:white_check_mark:
_any names starting with gl__	:white_check_mark:	:white_check_mark:
errors in vector component swizzling	:white_check_mark:	:white_check_mark:
erroneous octal number	:white_check_mark:	:white_check_mark:
numbers	:white_check_mark:	:white_check_mark:
comments	:white_check_mark:	:white_check_mark:
keywords (flow control, etc)	:white_check_mark:	:white_check_mark:
vector components	:white_check_mark:	:white_check_mark: