Embed copy of cram

We use the [cram](https://pypi.python.org/pypi/cram) Python module for command-line testing — i.e., where you want to run a command line program and verify its output in some way.  Before we relied on the cram module being installed in some system location.  But it's not very big, and it's only a single file, so lets embed it directly in the source tree instead.  Now you only need to have Python installed to be able to run the command-line tests.