2.2.1

This patch release brings several internal improvements, along with a pretty significant bug fix, and a couple of external upgrades for the ShadowsViewGroups.

• Previously, View shadows in the Foreground and Background planes ignored the parent ViewGroup's clipToPadding state, which would cause another kind of draw artifact for targets extending beyond the padded bounds of a parent with clipToPadding enabled. This behavior has been corrected with the current release.

• Most of the built-in lint checks for the base ViewGroups have been wrapped and augmented to work with the library classes, along with a custom check for some of the library's layout attributes. Details can be found on the ViewGroups wiki page.

• Each ShadowsViewGroup now registers its group attributes with the debug tooling, so they should show up in the layout inspector, per the documentation, though I've never seen any custom attributes there, even from Jetpack library Views.

  The individual attributes on the arbitrary child <View>s are not handled as such, currently. I'm not sure that it's even possible to do this there without some severe hackery.