Test for dependency cycle

Sudo check is done as early in the code as possible.

Changelog:
- Moved string colorization to lib/color.rb
- Moved constants to lib/const.rb
- Moved sudo checking before docopt checking.
- Changed docopt require to be relative
- Fixed stray tabs

Should be on CREW_PREFIX

The `${VAR:-/some/path}` will use the path on the right side if the variable on the left side is null or empty (ie if the user didn't set it).

miniupnpc is a lightweight upnp client library. Added as a prereq for bitcoin.

Tested as working on XE500C13-K01US.