Add NameResolver

[mtshiba]

Implement a name-resolver.

This allows for the separation of name resolution functionality from Context, as well as constant reordering and variable circularity checks.

TODOs:

• [ ] implement basic name-resolving
  • [ ] check referencing before definition
  • [ ] unused variable warning
  • [ ] deleted variable check
• [ ] implement constant-reordering
• [ ] circularity check