Add subcommands to Riff CLI

[aManNamedJed]

Right now riff can only create a Block, but it would be nice to add subcommands which would support other functionality.

Currently

$ yarn riff --name=TestimonialCard

Ideal usage

# Package installed globally

$ riff block:create --name=TestimonialCard

This would would open open other command possibilities

riff block:list
riff block:create
riff element:list
riff doc:create
riff doc:list
riff page:create
riff page:list
riff update
riff publish