All commits before this point are extracted from the `qd` repository.

The commits have been filtered to only include relevant files. I hope
this is a good compromise between squashing all history and having the
full history of another project attached to this repository.

This is a requirement for multi-hop network connections.

This fixes ghci.

There were some cases where the implicit Maybe was problematic, because
it was impossible to guarantee a value. This also improved the
`runQuery` return type (returning only an `Either` or an `Either e Maybe`
is semantically easier to understand than the old `Maybe Either`.

This introduced a lot of necessary changes, but the result is a better
`runQuery` API: Every Query is now answered with either an exception
detailing why the query failed, or with a result.