Fig compatibility layer 649

TODO deal with port edge cases, e.g. just container port specified, or IP and port specified on host
See http://www.fig.sh/yml.html
Issues have been raised for this missing functionality, which is not yet supported by Flocker.

Fixes #649
1. The stuff in the docstring is just documentation, it has no impact on the code (and vice versa). 
2. `unicode_literals` only impacts literals, not function parameters. If you call a function with bytes it will still be bytes that are passed in.

You should change the documentation to say it expects unicode parameters, but that needs to enforced by tweaking the YAML parser, probably.