Major code edition: Improved countfields in pu/iomisc, also added getname, findstring, and nextfield (nextfield removed from at_common.c).  In transit, made difference between isotopes (which come from linelist) and molecules (which come from atm file).  Created molecules and prop_mol structures.  Moved density and abundance from prop_isov to prop_mol.  Removed unnecessary variables from atm_data and isotopes.  Re-engeneered readatm to be simpler and independent of readlineinfo.  Propagated changes through makesample, cia, and extinction.  Fixed cross section misscalculation: use sum of radii of both colliding molecules rather than radius of only one of the molecules (factor of ~2 correction).  Added inputs/molecules.dat file with constant values of molecules: atomic names, atomic masses, molecular alias names, diameters, isotopic ratios (there is room for improvement in format).  Cleaning: deleted compiled files in pu, deleted at_common, heavily added comments.
Merge branch 'master', remote-tracking branch 'origin'