glcpp -- GLSL "C" preprocessor

This is a simple preprocessor designed to provide the preprocessing
needs of the GLSL language. The requirements for this preprocessor are
specified in the GLSL 1.30 specification availble from:

http://www.opengl.org/registry/doc/GLSLangSpec.Full.1.30.08.pdf

This specification is not precise on some semantics, (for example,
#define and #if), defining these merely "as is standard for C++
preprocessors". To fill in these details, I've been using the C99
standard (for which I had a convenient copy) as available from:

http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf

Known limitations
-----------------
Macro invocations cannot include embedded newlines.

The __LINE__, __FILE__, and __VERSION__ macros are not yet supported.

The argument of the 'defined' operator cannot yet include enclosing
parentheses.

The #error, #pragma, #extension, #version, and #line macros are not
yet supported.

A file that ends with a function-like macro name as the last
non-whitespace token will result in a parse error, (where it should be
passed through as is).