Clean up tests and bug fix

The tests were a bit messy by not using setUpClass. I've fixed that by using it.
In addition, the polymer code had an untested bug in that polymers_sequence
didn't work. I've fixed it but not tested that. A test should be added.
Fix problem with one sided internal loops

Internal loops with only nts on a single side would have the flanking pairs
reversed on the side without nts. This has been fixed as well as adding tests
for this case.
Bump to 0.1.0