Automatically configure bind directory

[ecdye]

We don't specifically need user input on a bind directory. This changes the zram-config API and ztab to no longer rely on it.

This is a major and breaking API change.

TODO:

• Add check for old ztab in update.bash
• Add checks in code to not break on old ztab format
• Create tool to migrate old ztab to new ztab (maybe automatically perform migration in zram-config)
• Add note to README