Feat/node insertion

[DieracDelta]

This is a draft PR for AST node insertion. Objectives:

• [x] create AST nodes for attribute sets
• [x] convert between Input type and attribute set
• [ ] clean code
  • [ ] so many places need &str instead of String
  • [ ] better file naming to match rest of project
  • [ ] clippy
• [x] tie into main control loop so we can create inputs
• [x] more tests

Resolves #18 and #14 .