Minor cleanup in nbt.go

Slightly less repeated code.  Moved declarations out of the loops at
least.
Moved tests from files to byte streams, all tests pass!

Created byte streams from the files, and now the tests pass
repeatedly.  Woo!  On the bright side, I can now put my tests on the
playground if necessary.
Removed no-longer-necessary test files.

Now that the tests have been converted to bytestreams, the raw files
are unnecessary.