The 'server.key' and 'server.crt' can printed to stdin.
The two options are:
`dokku certs:show <app> key > server.key`
`dokku certs:show <app> crt > server.crt`
This will create two files, `server.key` and `server.crt`.
Those files contain the private key and the certificate.
Includes tests.
This change removes all deprecated commands. In many cases, users have been warned for a number of releases before the commands have been removed. All commands that were removed have existing alternatives.
