Show a graph instead of a table for the ephemerides in the PDF output

BREAKING CHANGE: the JSON format has deeply changed to enhance its
consistency

You can now use the `--format=pdf` argument to save the data computed by
Kosmorro to a PDF file. The new `--output` argument must be given with
the export file path.

Colors can be disabled with the new `--no-colors` argument.

BREAKING CHANGE: the fields "details" and "ephemerides" have been switched.

BREAKING CHANGE: invoking kosmorro command without --latitude and
--longitude arguments will now only output the Moon phase and,
eventually, the events for the given date (or today if date not given).

BREAKING CHANGE: JSON format now returns the moon phase as an object
instead of a string