Parsing into structs from 3rd party crates

[rezural]

Hey!

I am needing to load from ply-rs into Vector3 from the nalgebra crate, but am running into issues not being able to define the PropertyAccess impl on a 3rdparty crate's structs.

Is this a known issue? Or is there a workaround? Any pointers are appreciated.

I will usually (almost always :D) be using a 3rd parties libraries Vector/Face implementations.. so having to create structs locally seems like a pain point.

Nice library, thank you!