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).

instead of "Planet" in the text format output

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