Feature request: Insert line numbers and file names

If you look in the GLES spec, and scroll down to the section called "Preprocessor" there is a bit on a very useful directive which I think could make glslify much easier to debug:

http://www.khronos.org/registry/gles/specs/2.0/GLSL_ES_Specification_1.0.17.pdf

It is the `#line` directive, and the way it works is that you can add in a preprocessor directive like:

`#line linenumber filenumber`

And then if you get an error the getProgramInfoLog will print out a sane/readable message. I think this could be integrated with gl-shader-core to produce human readable correct line numbers for glslified shaders.