Add dispass3 algorithm

The dispass3 algorithm allows the user to specify which characters may
be used to generate the passphrase.
Add support for chars in add command

Split the arguments a maximum of 4 times. This implies that the chars
property should _always_ come last (regardless of what may be added
later), so that the `:' can be used as part of the chars specification.
Add support for chars in generate command
Add support for chars in list command
Add support for chars in update command
Update docs