Fix the tests for the Carp 1.25 change to the error message format.

Carp (correctly) now puts the period at the end of the error statement.
Simplest way to fix that is to just use Test::Exception.  Might as
well pull in all of Test::Most while we're at it.
Run all the tests.
Fix the docs for running mite_shim.

Was goofing up calling it as a Perl function with calling it from the command line.