I baked the eof checking directly into the parser, rather than using
the skip and eof parsers. I also took the time to restore some tests
that were mistakenly commented out.
I wasn't able to abstract over `edn::Value` and `edn::ValueAndSpan`;
there are multiple obstacles. I chose to roll with
`edn::ValueAndSpan` since it exposes the additional span information
that we will want to form good error messages in the future.
