glcpp: Update README file (new specifications and fewer limitations).

The README file had grown a little bit stale. We've been using newer
versions of both the GLSL and C99 specifications, so list those. Also,
several of the documented known limitations have since been fixed, so
remove those.

src/glsl/glcpp/README

@@ -4,26 +4,28 @@ 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
+http://www.opengl.org/registry/doc/GLSLangSpec.Full.1.30.10.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:
+preprocessors". To fill in these details, I've been using a draft of
+the C99 standard as available from:
 
-http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf
+http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf
+
+Any downstream compiler accepting output from glcpp should be prepared
+to encounter and deal with the following preprocessor macros:
+
+	#line
+	#pragma
+	#extension
+
+All other macros will be handles according to the GLSL specification
+and will not appear in the output.
 
 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.
+The __LINE__ and __FILE__ 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