ENH: support 'get()' for retrieving argList options

- previously only had 'opt<..>()' for options, but 'get<..>()'
  provides more similarity with dictionary methods.
  The 'opt<..>()' method is retained.

applications/utilities/surface/surfaceClean/surfaceClean.C

@@ -96,7 +96,7 @@ int main(int argc, char *argv[])
     triSurface surf
     (
         inFileName,
-        args.opt<scalar>("scale", -1)
+        args.get<scalar>("scale", -1)
     );
     surf.writeStats(Info);