split apart dependencies of vaccine peptide selection

* added unit tests for individual ranking components
* vaccine peptide sorting by four criteria (mutant epitope score, negative wildtype epitope score, number mutated residues, distance of mutation start the edge of vaccine peptide)
* print and write FASTA of vaccine peptides with a little mutation metadata
* print epitopes associated with each mutation
Yeah, I was also uncomfortable with 0.0 and 1.0 being outside the user-specified function. But, I did specify in the docstring that the transform function should return values between these two extremes.