glcpp: Update README for new support of __LINE__ and __FILE__.

Drop these from the known limitations list since support was recently added
for these.

Also, fix a typo while in the area, (and the oddly missing final newline).

Reviewed-by: Matt Turner <mattst88@gmail.com>

src/glsl/glcpp/README

@@ -20,13 +20,11 @@ to encounter and deal with the following preprocessor macros:
 	#pragma
 	#extension
 
-All other macros will be handles according to the GLSL specification
+All other macros will be handled according to the GLSL specification
 and will not appear in the output.
 
 Known limitations
 -----------------
-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
 passed through as is).