Patches for subcommand work

A few changes to make this work for me:

 - Bump major version to `2` as this is a significant breaking change
 - Add the list of plugins to the help subcommand (the text was there, but didn't have any logic to print the list)
 - Re-introduce the `hiera?` method into the `Encryptor` class (this is used by hiera-eyaml-gpg - perhaps wrongly but I don't think this should be a breaking change)
 - Add a test to use the `eyaml recrypt` command and change the `recrypt` subcommand to never write decrypted data to disk
 - Removed some superfluous validation code in `edit` and `recrypt` subcommands