Module containing tools for resolving CDDL

Resolving the CDDL is a process of simplifying the representation to make further operations, such as CBOR generation or validation, easier. We operate with a number of passes:

1. First, we deal with any rule extensions and create a single map from identifiers to (potentially parametrised) entities.
2. Second, we flatten the structure to a CTree, which discards a lot of the extrenuous information.
3. Then we resolve identifiers. Specifically, we do three things: - Resolve identifiers that map to the postlude. - Differentiate between generic args and references to top-level rules. - Validate that all references exist. Note that we cannot resolve all references since they may be circular.
4. Finally, we monomorphise, synthesizing instances of rules with their generic arguments bound.