Now the material node is aimed at Godot's SpatialMaterial. Textures are generated and passed to the SpatialMaterial (and not generated as shaders anymore).
Rendering textures requires a Timer (to wait for the viewport to be rendered). There has to be a better solution...
Added a couple more examples.
Added Image node that can be used to import textures
Renamed all get_shader_code methods to _get_shader code so a caching system can be integrated in node_base (and we can get rid of get_source_rgb and get_source_f functions)
