Remove the delayed-hide of previous content state

This effectively reverts the intent of b9503be6.

The concept of delaying the hide of the previous content state is
causing more trouble than it is worth, resulting in several race
conditions.  Rather than resolve the race conditions, it is more
prudent to remove the delayed hide entirely, as there is no reason
to think that atomically swapping visibility would be broken.
Resolve more issues related to restoring view state.

Also adds logging in the debug variant via `BuildConfig.DEBUG`.
Starts publishing both release and debug variants so that applications
can make use of the debug variant if desired.

Introduces support-annotations dependency so that host applications
can receive `@Nullable` and `@NonNull` hints in the IDE.
Merge pull request #8 from jhansche/master

Remove the delayed-hide of previous content state