Matrix extension: Implement eigen-related primitives

[LaCuneta]

The Matrix extension was cleaned up and shipped, but one issues remains, as per Jason's comments from #197:

There are three primitives that are entirely unimplemented, all of which pertain to eigenvectors: real-eigenvalues, imaginary-eigenvalues, and eigenvectors. There is an issue here, since the otherwise-good matrix library that is being used (Vectorious) does not currently support eigenvector operations. The author has stated numerous times that he intends to implement those things at some point, but... it's been a while; who knows if it will ever happen.