Previously, when parsing config options that were set to 'false',
e.g. `TOPEN_NOTES_QUIET=false` in the env vars,
we would still be setting it to true.
This change fixes any falsy value to be correctly parsed as False.
Since we can set the type of the relevant option in the OPTIONS dict, we
should also let the cli correctly cast them on parsing, just as the env
options do.
