- Almost everything 0.15; also servant-foreign jumped to 0.15, for
consistency
- Bump lower bounds of dependencies to most recent versions atm
- Use hspec-2.6.0
- Update `stack.yaml` accordingly
- Use base-compat a bit more
- Drop aeson-compat dependency (in tests and tutorial)
We use NoContent to signify an empty response nowadays. This commit
replaces all occurences of () with NoContent so that all packages use
the new semantics.
