Revert "Throw a descriptive error for collectionViews"

This reverts commit 1df40a88f3e34a10cfabd07135669099cbac94bc.
Bump and build v2.2.1
Update upgrade guide to follow semver
Update marionette.functions.md

added item about proxy unbindEntityEvents - 'Marionette.proxyUnbindEntityEvents'
Update marionette.itemview.md

The old example for 'variable' in the documentation did not work for me. The 'settings' argument is the 2nd or 3rd argument of the _.template function. The model is then passed in as a parameter to the then generated template function. I attempted to update the documentation to reflect this.
Improve comments in region.show. Small cleanups.
Update marionette.object.md

updated 'Basic Use' item
Fix broken logo path