Support for non-git buildpacks

[szymonpk]

Currently BUILDPACK_URL has to be a git repo.

There is (at least one) a buildpack which is distributed in pre-complied form (*.tgz). It's possible to pass link to the archive in heroku, buildpack in git requires some manual action (complication), so it won't work in Workflow.

Is it possible to re-implement this in Workflow?

As workaround I've unpacked provided archive and pushed it to separate git repo.

[bacongobbler]

Sure, if someone wants to implement .tgz and .tar.gz support for BUILDPACK_URL it can be done here. One would just need to check the file extension and do a HTTP GET if it's a tarball (.tar.gz or .tgz extension), otherwise perform the regular git clone.

[Cryptophobia]

This issue was moved to teamhephy/slugbuilder#4