Add custom-setup stanza and containers lowerbound

custom-setup:

- http://cabal.readthedocs.io/en/latest/developing-packages.html#custom-setup-scripts
- https://www.well-typed.com/blog/2015/07/cabal-setup-deps/

Bounds:
- containers-0.5 is required if Data.Map.Strict
- parsec-3.0 for Text.Parsec
- json-0.3.6 for makeObj