dbparams should have an option for the SQL alchemy url format

[adamchainz]

As used by https://github.com/dbcli/mycli.

[adamchainz]

N.B. https://github.com/simonpercivall/django-dbshell-plus performs the main use case I thought of (launching mycli for your db). However it woudl also be useful for sqlalchemy powered libraries like https://csvkit.readthedocs.org/en/0.9.1/scripts/sql2csv.html