Add a performance test

[sebastian-philipp]

We should add a performance test using criterion to detect bugs like #93 in the future. Mabe we can use travis-ci for executing a performace test that fails, if that takes longer than the last run?

[chrisreu]

Yes we should do that.

I think, we should use the latest Criterion library for that. It not only tracks running time now but also provides memory statistics.

We could define upper bounds for both runtime and memory usage for specific tests and then let criterion verify that.