Fix the encrypt action

The action previously tried to use code for formatting the output (according
to the --output option) even when it was transforming a eyaml file. This made
no sense and resulting in a series of exceptions and problems.

Added a test that encrypts using the command that previously broke for me.
Add logging to encryptor class

Make it really easy for encryptors to log sensibly. These were in
the gpg encryptor but really belong in the base class.

Also refactored the plugin_classname for reuse.
Merge branch 'sh-add-encryptor-logging' of https://github.com/sihil/hiera-eyaml into sihil-sh-add-encryptor-logging
Tweaked readme
Updated version number to 1.3.4