Manage string embedding and the glsl compiler and language options.

This is somewhat separate to the main GLES code and can be used without linking to any system dependent GL libs.

verr,ferr = glslang.lint_gles2(vcode,fcode)

Try and compile a vertex/fragment shader pair and return any errors.

returns nil,nil on success or an error string if either shader fails to compile.

Note that the glslang compile step seems rather slow, not sure what it gets up to but do not consider using this if speed is important.

shaders=glslang.shader_chunks(text,filename,headers,flags)

    load multiple shader chunks from a single file and return a lookup
    table of name=code for each shader we just loaded. These can then be
    compiled or whatever.
    
    set flags.headers_only to true if you only care about parsing headers
    for later inclusion and do not want to parse shader chunks.
    

#SHADER "nameofshader"

    is used at the start of a line to say which chunk the following text
    should go into. This is technically the same as #header but makes it
    explicit that this should be all the code for a shader rather than just
    a piece.

#HEADER "nameofheader"

    can be used to define part of a shader, which can later be included in
    another shader by using

#INCLUDE "nameofheader"

    Will insert the chunk of text previously defined as a #SHADER or #HEADER

#SHADER or #HEADER

    without a name can be used to ignore the next part of a file, any text
    at the start of a file before the first #SHADER or #HEADER is also
    ignored. This enables these chunks to exist inside comments in a lua or
    whatever file.

code,err = glslang.pp(code,err)

Preprocess a vertex/fragment and return the result.

returns nil,error on error

process #include statements in src with strings found in the headers table

parse a shader source and yank any #version out of the source and into a table this allows multiple attempts at compiling the same source using different #versions