Link to the correct location for the databags API source

Add the public Github location

Merge pull request #2 from kvandervliet/berks3

Use the new 'sources' scheme for finding the 'Databags' API endpoint

Retrieve the array of cached cookbooks correctly (includes the Cookbook at '.', for example)

Use Berkshelf 3 API

Pass an option that's needed by the method we're testing; avoids spurious failure

Berkshelf now demands at least one 'source' so run tests that require a Berksfile with a dummy version instead of /dev/null

Use Berkshelf 3.0

Update documentation to cover the API & 'databags' directive

Use stderr for debug messages

Output debug logs to stderr

Use the logger for output

Improve the output of the list command

Make the list option more flexible