Rename application to main
Update b12, add option for no sweep.

Change b12 function in ohcalcs:
- Convert degeneracies to float to avoid subtle in division errors
- Stop using 'nu12' as default freq argument.

If stype of Sweep is not 'sin' or 'saw', assumes that should mean sit
on the middle of the absorption feature. Quick and dirty change, doesn't
deal with alignBins, which leads to fictional values for irrelevant vars.