ENH: simplify method names for reading argList options and arguments

- use succincter method names that more closely resemble dictionary
  and HashTable method names. This improves method name consistency
  between classes and also requires less typing effort:

    args.found(optName)        vs.  args.optionFound(optName)
    args.readIfPresent(..)     vs.  args.optionReadIfPresent(..)
    ...
    args.opt<scalar>(optName)  vs.  args.optionRead<scalar>(optName)
    args.read<scalar>(index)   vs.  args.argRead<scalar>(index)

- the older method names forms have been retained for code compatibility,
  but are now deprecated

applications/utilities/postProcessing/postProcess/postProcess.C

@@ -143,7 +143,7 @@ int main(int argc, char *argv[])
 
     #include "setRootCase.H"
 
-    if (args.optionFound("list"))
+    if (args.found("list"))
     {
         functionObjectList::list();
         return 0;
@@ -155,13 +155,13 @@ int main(int argc, char *argv[])
 
     // Initialize the set of selected fields from the command-line options
     functionObjects::fileFieldSelection fields(mesh);
-    if (args.optionFound("fields"))
+    if (args.found("fields"))
     {
-        args.optionLookup("fields")() >> fields;
+        args.lookup("fields")() >> fields;
     }
-    if (args.optionFound("field"))
+    if (args.found("field"))
     {
-        fields.insert(args.optionLookup("field")());
+        fields.insert(args.lookup("field")());
     }
 
     // Externally stored dictionary for functionObjectList