Rename all files to arethusa_cli
Add generate subcommand
Fix namespacing issues in Thor

Thor refuses to write the correct banner. It's still workable though
when we override the banner method and use namespaces for our
subcommands.
Minor reformatting
Extract thor subcommand patch to own class
Update README
Last and hopefully final renaming
Merge pull request #2 from latin-language-toolkit/cli

Rename to arethusa-cli