MHCflurry 2.3.16

MHCflurry 2.3.16

mhcflurry-predict now accepts an input CSV in which a flank cell is empty,
as it is for a peptide at a protein terminus. pandas previously read the empty
cell as NaN, and prediction failed with ValueError: Sequence of strings is required. Flank strings such as NA and NAN, which pandas also read as NaN,
are now kept as sequence.

The prediction models and numerical prediction behavior are unchanged.