Options updates.

A number of options changes to improve consistency.

- New option `--colors` is on by default can be switched off with `--no-colors`, removing the colored terminal output in most places.
- Remove command `empty` and Server options `--force` and `--cachesecs` in favor of a duckpan option of `--empty` which empties the cache at start-up
- Option `--no_check` becomes option `--check` which can be switched off with `--no-check`.  `--no-check` now emits a notice and does not check _any_ requirements.
- Add documentation strings for all extant options which are shown with `--help` at the appropriate level.