Upstream and generalize parser/quasiquoter for LLVM types

[robdockins]

The crucible-llvm package now (as of PR #376) contains a quasiquoter for llvm declarations that is used to significantly reduce the boilerplate burden for defining intrinsic functions; it is found in Lang.Crucible.LLVM.QQ. The llvm-pretty package also contains a parser for LLVM type syntax that is used in saw-script to allow easier building of llvm types.

Currently, the crucible-llvm parser adds to the base syntax the ability to have quasiquoter metavaraibles that will bind program variables in the program souce, which the llvm-pretty parser does not have. However, it might be useful also for saw-script to be able to bind variables in those declarations.

It might make sense to unify/generalize these two systems rather than have two similar systems implemented in different places.