Add some of CLTL2's environment extension facilities, redifine metadata using these

[cbaggers]

Our metadata turned out to fit really nicely into declare. Looking at https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node102.html I realized that implementing a lot of this would be fairly easy. It's a generalization over what we have but I think we can get pretty close.

We can then define the metadata api over this.

NOICE