Allow overriding the JSON parser used.
Be more strict testing for queries in `r()`.
Add tests for overriding the JSON parser.
Add a logging function for warnings and errors.
Replace `error` with `r._logger`.
Add warnings for `userdata` and `threads` being sent to queries.
Let CI test the JSON override.
Add `dkjson` to the optional dev dependencies.
Add ReQL admin terms.
Release v0.6.0.