* Use specific revision to build xpi and return download URL in pingback
* Add --harness-option builderVersion=PackageRevision.pk to xpi command
* add ability to override manifest attributes with package_overrides
* add option to change sdk used to rebuild an existing PackageRevision
* api_builder doc added
branch repackage_builder_addons
bug https://bugzilla.mozilla.org/show_bug.cgi?id=699509