Support `todo` as alias for `todo('')`

A TODO reason is often helpful but I don't want to enforce that policy
on users who are just doing some quick prototyping and don't need to
give themselves a reason.
Support small tests with an implicit name

For many tests, the test body itself is the best name that can be
given.  It's obnoxious to manually keep the head and body in sync.
One can now omit the clause head and both the head and body will be
generated from it.
More descriptive pack title
Bump version for release