Simple "Literal Analysis" in Typechecker

[gilbo]

We want to have a way to throw type-checking errors when certain accesses use non-constant values.

We want this for Affine-Indexing, and also for indexing into vectors and matrices. In the latter case, we want to be able to have loops over constant ranges generate indices with known bounds (i.e. not constant, but something we can certify is ok to index with statically.

Also, this issue may be related to #34 which handles a special form of constants: strings, which can't be manipulated with computation/arithmetic anyway.