fix logging of readable regexps

define #inspect and #to_s on the object itself instead of subclassing
Regexp, which can have weird behavior as it's a core Ruby class

previously, the regexp couldn't even be logged as #to_s would fail

Change-Id: I55e62a4cedc0d2f4d8f81af901ec55b4f6d2dc14
Add buildpack attribute to app

- used for specifying a custom buildpack location
- URI is validated as either git://, http://, or https://
- private URIs fail validation as expected

Change-Id: If0edf59edc9b60d8a61b3e9901fcc94a513d41e2
Merge "fix logging of readable regexps"
Merge "Add buildpack attribute to app"