Improved parallax mapping. Generate heightmaps on the fly.

client/shaders/nodes_shader/opengl_fragment.glsl

client/shaders/nodes_shader/opengl_vertex.glsl

client/shaders/water_surface_shader/opengl_fragment.glsl

client/shaders/water_surface_shader/opengl_vertex.glsl

minetest.conf.example

src/clientmap.cpp

src/defaultsettings.cpp

src/mapblock_mesh.cpp

src/mapblock_mesh.h

src/mesh.cpp

src/shader.cpp