Initial README

Add grab-bag of useful utils onto expressions

Add a Dhall.dump

Add experimental json/yaml to dhall scripts

Fix to_cbor usage

nil hash values are omitted from record

Add Dhall.load

Add as_dhall refinement

Add SimpleCov

Test typechecker edge cases

Optional#value is not what we want here

Update makefile with more helpers

Run all dhal-lang typecheck tests

Run all dhall-last tests for cache_key

Run all dhall-lang tests for normalization

Pass all import tests

Allow self-describing CBOR

Environment variable failure can fallback

Allow imports to be either binary or source form

Tests are in UTF-8