In the current API, there isn't a possibility to create your own shaders (they get chosen automatically depending on what texture maps you specify for a material, like normal/parallax/specular maps). I might make a somewhat easy to use system for custom shaders. Assuming that I'll write a deferred renderer at some point, that feature will might/will be gone for a few or more releases though (assuming that I'll have it implemented by then which is very unsure), since deferred rendering is the most inflexible system ever xD.