Drop Rails dependency down to 3.0
Attempt to load CacheDigests unless ActionView::Digestor
Check for precompiled asset digests in Rails 3 & 4

Using the Rails::VERSION is an ugly hack. Need to come up with a better
solution.
Update Fixtures to get around our ugly hack.
Attempt to set #template_digestor late

In case CacheDigests::TemplateDigestor load after Ettu.
Bump version to 0.0.8