add test suite

[Birnendampf]

this might be rather tricky as it would require lots of dummy files

[Birnendampf]

This is becoming a problem when trying out new nbt parsers

[Birnendampf]

We are now at 95% branch coverage now. while this is still not done I can finally move on and work on some more interesting stuff, keeping this on the back burner. What surprised me is just how many bugs the big test push in #29 unearthed