Add aws/cloud_formation_single_ubuntu_instance_register_hostname_in_dns
Ignore creds.env
Can't use _ in stack names.
Activate the dpcode virtualenv for the code. This is for mocks.
Add a mind-map of how the exercises build on each other.
Ignore scratch_spec.rb
Add python/determine_sequence_additions
Add python/determine_sequence_additions_preserve_ordering
Rename determine_sequence_additions to determine_sequence_additions_set
Add python/determine_sequence_removals_set
Add python/determine_sequence_removals_preserve_ordering
Add description to HostName output variable.