adding timevarying covariates to AAF and refactoring the whole of it. Adding NotImplemntedExceptions to things that aren't working yet. No tests yet
previous tests passing/updated for new apis
bumping release
updating docs and plotting for aaf"
some inline documenation
tests and some code funness
Adding new aaf plotting tests, adding BayesianFitter
merging Nick's PR, and adding #37