major overhaul of svg mesh rendering/shader handling, add lambert & phong shaders, update examples

shaders now implemented using PShader protocol w/ support for uniforms & renderer hints/flags (only :solid so far)
disable hidden surface removal if shader is not marked as solid
separate facet z calculation from project-faces fn to avoid effort for any culled faces
shading fns now only work with normalized RGB, final RGBA color format done by actual shader
add translucent shader wrapper fn