htslib unittests

If you look at my test file for hts_endian.d, I just ported over the test cases from htslib. It would likely be to our benefit to port over other htslib tests to ensure that the bindings are functioning as intended.

After revisiting this, should probably only port tests for ported inline functions from htslib (see source/htslib/test/hts_endian.d, and source/htslib/test/kstring.d). No reason to test all bindings.