TODO: document the setup of the IntoWand and WandWeaken type classes
and the tricks using Hint Mode.

This fixes issue #65.

Also, give names to hypotheses that we refer to.

Also add "Local" to some Default Proof Using to keep them more contained

This fixes issue #67.

It now copies the hypothesis when: 1.) it is persistent 2.) when destructing
it requires a universal quantifier to be instantiated. The new behavior is
implemented using a type class (called CopyDestruct) so that it can easily be
extended.

This fixes issue #51.

This fixes issue #62.

The error message accidentally got removed in e0789039.

wp_apply often results in an of_val that should be simplified.