The beginnings of some command line testing code.

It strikes me that app/tests/lib is browser oriented so maybe having
app/tests/command-line is handy for tests which can run using only the
metapolator command line tool.

The fontforge-export-subset.py file is a utility that allows you to
cherry pick one or more glyphs from a font and export the result to a
new UFO file. Handy when you are only interested in a specific subset
of glyphs and don't want to congest the machine by having metapolator
work on glyphs that you are not interested in for the test at hand.

The command-line/interpolate subdirectory contains the start of a test
for non-glif interapolation. I started with test.sh and then moved that
to test.js so that xpath evaluation and other tools are supplied by
npm instead of various third party binaries on the system.

The test.js uses nexpect and xpath to start processes and test various
XML files in resulting UFO files by checking if nodes at specific locations
exist and have an expected content.

interpolate-for-non-glif-investigation.sh remains a shell script, it
is mostly a series of calls to the metapolator command line tool to
perform work.

Comments and suggestions welcome.
IMHO metapolator init is a little different to overwriting a zero sized file if UFO was a single file format. It is likely that folks might say "/tmp/foo" is where I want my metapolator project, so I'll make that directory and then tell metapolator to initialize that as a project/workspace. As long as I can then tell metapolator that the project is at /tmp/foo I don't really care if mp creates a subdir or how it structures the tree under /tmp/foo. Setting up a project somehow feels a bit different to saving a single font file. 

It's not a big concern for me personally, because I'm now aware of how to use the command. I only mentioned it because it might catch out others.