Allow Symbol in yaml-to-dhall
Update handling of builtins

Always parse to a special value and not to variables.
Encode seperately.
Remove empty re-opens from normalize
Normalize text concat as interpolation
largeExpression works now, but is slow

So only run in CI
Update dhall-lang and work with the new ABNF
as_dhall for Symbol
Parse expression from ENV var import

Instead of the path-only support from before.
Standard reader requires UTF-8

To disable heuristics, force remote content to be UTF-8 text.
Fail fast when encoding is bad
Speed up tests by not resolving when not needed
Test everything the README says
Change list of unit tests
to_a keeps elements as Dhall
Clarify that the README is the authority
Add build instructions to README
Downgrade to GPL