Test suite must actually build some fonts

[alerque]

I don't know how to lay this out (external demo repositories? script to generate them internally? tarballs?) but one way or another the test suite for fontship itself must include generating fronts from various different canonical sources. Already I've broken master multiple times with unexpected side effects that don't impact the thing I was testing but do affect other font projects. Testing that fontship itself builds and runs isn't enough, it needs to generate expected results from actual font sources.