Just minor documentation changes

Simplify documentation, bump version

Remove the "creates and destroys snapshots only when it makes sense"
note and the associated footnote.

0.4.0: Always create snapshots

Prior to this commit, zap would only create new snapshots for filesystem
that had changed since the last snapshot.  If there were no changes,
then the name of the most recent snapshot would be updated with the
current date.  There were problems with this logic, so just
unconditionally create the snapshot.

Version 0.3.0

The Command line arguments were simplified in version 0.3.0.