Refactor AnonymousType typecheck

Refactor Record typecheck

Refactor RecordSelection typecheck

Refactor RecordProjection typecheck

Refactor Union typecheck

Finish merge refactor

Refactor Function annotate

Refactor Forall typecheck

Refactor some of typecheck

Get closer to fitting the metrics

Run tests per docs

Clean up style violations

Use path like names in more tests

Implement integrity checks

Always encode OptionalNone in new style

Flatten/unfill applications and builtins when encoding

Remove multi-argument applications

They only exist in binary encoding, so let's keep them there.

Working typechecker

Type inference/checking about half done

Passing unit tests for features implemented so far

Support headers for HTTP import

Binary encoding

Every AST node uses as_json to express the generic structure for
encoding itself.  Expression aliases as_cbor to as_json by default and
then uses as_cbor in to_cbor (aliased as to_binary).

This design is because we need to override the encoding of Double for
CBOR, but want to keep the normal Float value for as_json in case that
is used directly (to avoid surprising the user).