document command prints to stdout

The command is now able to print to `stdout` so that we may redirect
its output somewhere else. If we want to write straight to file then
we can use the option `--output-dir`.
style init update

Dropped the valid keys array and substituted it for a required keys
array. There are some optional keys which by default are set to None.
The developer may now add any other piece of information to the style.
cloud command

the cloud command takes care of the registration of lexor packages.
More work is required in the list subcommand. A function used by the
install command will be needed.