* name keys after emails, not usernames
* use emails to specify users
* rename and add function to get emails from keyrings
* rename directories holding gpg test fixtures
* deny emails that aren't in the keyring, and test.
* require 'killperson' emails to exist in keyring
* change test to reflect killperson must use email
* remove no-longer-needed test function
* factor function _assert_keychain_contains_emais()
* fix/make lint happy
