Blender Git Loki

Store particle index and randomized value from particle instance
modifiers, for use in shaders.

The particle instance modifier can now store 2 custom data layers:
- Index: the integer index of the particle
- Value: a randomized floating point number for shader variation

These layers have user-defined names, so multiple particle instance
modifiers can be used without overwriting customdata layers. In Cycles
the data can be accessed using an Attribute node with the same names.