Add `diesel drop` to the CLI

[mcasper]

We should have some way of dropping the user's database in the CLI, for whenever the user wants to reset their data or their schema. This command could be diesel drop, diesel drop_db, diesel drop_database... This would allow the workflow of diesel drop; diesel setup to reset your database.

My thought of what it should do:

• Drop the database specified in the user's database-url string.

If we like this, I'll go ahead and implement it this afternoon.

[mcasper]

Or maybe database should be a subcommand, and then have its own derivatives. So it might become

diesel database drop
diesel database setup
diesel database foo

[sgrif]

Is there any use case for just drop on its own? Should we just have this be diesel database reset?

[mcasper]

You know, I can't immediately come up with a use case for drop on its own. Maybe just reset for now, and see if legitimate use cases for drop come in

[sgrif]

Just to clarify, my reasoning here is that we definitely want reset as a command either way, and I'd rather not expose drop on its own without a specific reason, as it's just one more thing to maintain and/or change if we ever decide to do something like rails/rails#22967

[mcasper]

Resolved by #161