Initial commit using methadone

This is not fully functional, just:

- adding methadone
- creating the initial executable using methadone (only walks vdcs)
Small changes to gemspec
Make output a bit more informative
Add resource options to usage

It's not clear how to do this correctly using methadone so I've added it to the general readme so that at least it's there. @mikepea perhaps you can advise?
Add all existing thor functionality to methadone

This is WIP, e.g. there is no test for the new method I've added in walker.rb; the error message is not informative, etc. Am committing this so that rest of team can see where I am going with this.
Merge branch 'master' into methadone
Move print to bin/vcloud-walker

This makes walk method testable. Also adds a test for it. It's not a great test because the data is mocked, but it acts as a check that the correct methods are being called.

The error message when not one of the valid calls has been removed. Will be returned in a later commit.
Add back error message

It is just being printed out here. Could be handled more elegantly.
Change all method to organization

To enable removal of case statement in walker.rb. This is the only method name that differs from the input.

I have changed this in Thor as well, though the plan is for Methadone to replace Thor.
Replace case statement

Thanks @snehaso!
Merge pull request #37 from alphagov/methadone

[#61991106] Add methadone