(Mocha has a 'bail' config flag that's supposed to do this, but it doesn't seem
to work when passed to mocha.setup() (maybe because we're setting a custom fail
handler?), so this just calls abort() on the runner manually.)
Implements the beginnings of unit testing infrastructure using
mocha/chai. The unit tests can be run locally using test/runtests.sh,
although this will need tweaks to run on Windows. They should also run
on commit using Travis-CI.
The unit tests themselves live in test/tests. The index.js file
specifies separate test sets, which can be run individually by calling
test/runtests.sh <testsets>. Right now there is only a single unit
test, but hopefully we'll have more soon...
