Added a new flag HLSLCC_FLAG_COMBINE_TEXTURE_SAMPLERS which creates a ne...

Added a new flag HLSLCC_FLAG_COMBINE_TEXTURE_SAMPLERS which creates a new GLSL sampler for every unique texture+sampler pair used in HLSL.
The new sampler names are the texture name and sampler name delimited by '_X_'.
For example, the HLSL code "diffuseTexture.Sample(linearSampler, texcoords);" will become a GLSL sampler named "diffuseTexture_X_linearSampler".
The delimiter '_X_' is used so other code can easily split the GLSL sampler name into the original texture and sampler components.