Using the Cmd() class to print the welcome screen

This allows us to slowly add the Cmd() class for command line
interpretation.
[features] using "given" for program start test

This is somewhat forward-looking.  I want to reuse this code in a future
test which will need to be a "given", and having this test use "given" isn't
a bad semantic change.
[features] using nose.tools for better assert statements
[features] adding vim coda and replacing hard tabs with spaces
[features] adding tests for a prompt and faking the implementation
[features] matching method name better to purpose
Skipping "wip" scenarios when running behave
[features] adding the exit command scenario

... and boilerplate step methods
Making the 'acceptance' target also PHONY
[features] correcting minor typo
Adding the 'exit' command

Now the cmdloop() can run and we're getting closer to a program which
actually uses the Cmd() class in a real way.
Merge branch 'master' of github.com:paultcochrane/HannoverHotspots