Complete basic nwchem input file parser - only works with files generated using
NwInput for now.
Better error def.
Vastly improved parser for NwInput.
Greatly simplify nwchem string parser.
Minor cleanup of nwchemio and tests.
Fix mutable argument.
Remove print.
More code simplification.
Do not artifically set start directive in nwchem input.
Add options to set geometry optinos.
More updated geometry options code.
Simplify the base NwTask class.
Updated docs for v2.7.5 release.
Changed return ValueError to raise ValueError in substitutor.
 Cosmetic changes