For use with bevy 0.13

See for reference:

https://github.com/bevyengine/bevy/blob/v0.13.0/crates/bevy_pbr/src/pbr_material.rs

https://github.com/bevyengine/bevy/blob/v0.13.0/crates/bevy_pbr/src/render/pbr.wgsl

This also swaps out any instances of the standard material with the custom included material. (see swap_standard_material())

Also see https://github.com/DGriffin91/bevy_mod_standard_material/tree/minimal for a minimal version.