heroku-buildpack-ruby

Emit more best practice warnings.

Instead of waiting for users to do bad things, and open support tickets to tell them about best practices, lets be a bit more proactive. 

Using asset_sync is bad, don't do it.

Using RAILS_ENV=staging is bad, don't do it.

Switching all HEREDOCS in ruby.rb to `<<-` so my editor parses them correctly.