Boot2docker config

contains #91, please ignore the Makefile change..

I'm not 100% sure that the `$ENVVAR` expansion in an ini file makes sense long term - please, discuss?

My interest here was to make it easy to create a default profile file, and then as I was working on it I was talking to @crosbymichael, and he suggested I should look at using the toml library for parsing the profile file. I think I like it as a simplification of our marshaling code..