This commit does kind of a lot to get cass(1) over the finish line.
For one it implements all the CLI functions (well, almost all) with
their respective parameters, and also creates a new `gen` module which
uses the IR stream to generate a new file based on the old one, while
updating header fields that need to be updated (currently only
`version`).
This version does nothing with the actual header values, and probably
has a lot of bugs. More documentation will follow in future
cassiopeia commits.
Katharina Fey