First pass at import resolution
Tests are long for good reasons
Builtins are part of the standard set
Make every Expression a ValueSemantics and use the known list of
attributes to map generically over any AST node.
Introduces a conditional, but removes boilerplate from every single
Internal flag to disable for acceptance tests from the standard (which
assume beta-only normalization in some cases). Otherwise, just always
alpha normalize as we go.
Update to latest binary format
Migrate to dhall-langv6.0.0
Use git-extras for `git root` in build
Bare minimum refactor to pass the metrics
Pass most compliance tests
No import or multiline string support yet
Beta normalization complete