Open Fission Product Yield Data

This implements an open access version of fission product yield data coming from WIMSD [1].  This data is redistributable.  It will be worth investigating the NDS data as well [2], but this was most expedient. 

1. https://www-nds.iaea.org/wimsd/
2. https://www-nds.iaea.org/sgnucdat/c2.htm