Updated to be essentially working mapping of u_kln to u_kn.
Added a test script that works with the updated u_kln->u_kn code.
Manually adding a change to make manual merging easier.
resolving issues between master and nk, all in pymbar/__init__.py
Address a number of issues raied with the pull request.
Merge pull request #83 from mrshirts/nk

Extensive conversion from u_kln->u_kn formalism.  Still need to debug `import version` issues with travis-ci.