Minimal support for OpenGL ES.

Currently only XML parsing and function extraction, no ES-specific
changes in template files.
Less optimistic stripping of duplicate commands.

Currently in the gl.xml file there is duplicated glGetPointerv() in GL
4.3 and also glProgramUniformMatrix4fvEXT() in
EXT_separate_shader_objects ES extension. It's thus needed to remove
duplicates also inside the subset itself.
Changing use of version.core to check of version.profile in templates
Merge branch 'duplicate-commands' of https://github.com/mosra/flextgl into gles
Merge branch 'testing' of https://github.com/ginkgo/flextGL into testing