Define full set of config vars

[ehmatthes]

Right now there's only one config var, AUTOCONFIGURE_ALL. That's been good enough to get started, but I need more in order to handle the range of approaches to autoconfiguration that people will need.

Define the full set of config vars, and then implement them.

[ehmatthes]

• AUTOCONFIGURE_ALL
  • With this, a set of vars for disabling any individual aspect of auto-configuration:
  • Procfile: No need for disabling auto configuration of Procfile, since it will skip this step if one is present.
  • Allowed hosts: No need to deal with this, since it's only overwritten if it's currently empty.
  • Database: DISABLE_AUTOCONFIGURE_DB.
  • Static files: DISABLE_AUTOCONFIGURE_STATIC_FILES

Now that I write this out, there really isn't that much to do. I thought there might be need to add more flags for just auto configuring some aspects, but there are so few pieces here it's not really needed, and would just make things more complex. So final docs would be: "Turn autoconfigure_all on, and then disable auto configuration of database or static files if needed."

[ehmatthes]

Technically, this buildpack doesn't even need the AUTOCONFIGURE_ALL flag. Since people are choosing this buildpack, it could just do the autoconfiguration unless there's a flag to skip a step. But this is meant to show how the default buildpack could be made to automate almost everything, so I'll keep the main flag.