Improve testing coverage

[eirikurj]

We need to improve testing coverage, both in terms of unit and regression tests. Currently, we only run regression tests using the examples found in the examples directory. Furthermore, these test are limited in scope as they only cover block size and topology. Changes in BCs and coordinates are not captured in the current tests.

[sseraj]

Changes in BCs and coordinates are now captured now that we use cgnsdiff (#54)