Add tests

[timodonnell]

Would it be feasible to add tests that run epidisco locally on a small set of reads and verify that the expected variant calls are made? We generated data like this for guacamole (see e.g. here and here), which could potentially be used.

Having tests would hopefully catch issues like #128

[smondet]

Just noting: #128 is just command line parsing → could be caught with --dry-run option (no need for data or a Ketrew server to submit the pipeline).