Changelog for covenant-1.2.0

Changelog for `covenant`

All notable changes to this project will be documented in this file.

The format is based on Keep a Changelog.

Helper function for safely retrieving an in-scope type variable when constructing the ASG
Removed Return nodes, associated pattern synonyms, and the ret ASGBuilder function
Reworked the renamer to be context sensitive
Added new error types for un-renaming
Modified ASG helper functions and updated tests to conform with renamer rework
Added support for introduction forms (ValNode stuff, ASG helper function, tests)
Added support for catamorphism elimination forms
Added support for pattern matching elimination form

Representation of datatype declarations and datatype types
Generators for various flavors of data declaration and value type
A "kind checker" which serves as a basic sanity check on datatype declarations ingested by the pipeline
Base functor transformation machinery
Tests for the base functor transformation
Misc internal helpers to support the above functionality
Ledger type definitions for use in the ASG
Support for primops over data types
Support for arity-six primops in the ASG

Initial version