BNL_nuclear_wallet_card.dat was downloaded from the BNL "nuclear wallet card search" 
https://www.nndc.bnl.gov/nudat3/indx_sigma.jsp

We use it to get the nuclear spins of each isotope, so that we can adjust molecular partition 
functions from the "physical" convention, which includes nuclear spin degeneracy, to the 
"astrophysical" convention, which doesn't.

reformat_nuclear_wallet_card.jl is a script that parses the file and outputs a nicely formatted 
Julia dictionary, which is appended to src/isotopic_data.jl.