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/mesh/manipulation/mergeMeshes/mergeMeshes.C

@@ -97,20 +97,20 @@ int main(int argc, char *argv[])
          FatalError.exit();
     }
 
-    const bool overwrite = args.optionFound("overwrite");
+    const bool overwrite = args.found("overwrite");
 
     fileName masterCase = args[1];
     fileName addCase = args[2];
 
     const word masterRegion =
-        args.optionLookupOrDefault<word>
+        args.lookupOrDefault<word>
         (
             "masterRegion",
             polyMesh::defaultRegion
         );
 
     const word addRegion =
-        args.optionLookupOrDefault<word>
+        args.lookupOrDefault<word>
         (
             "masterRegion",
             polyMesh::defaultRegion
@@ -166,7 +166,7 @@ int main(int argc, char *argv[])
     const bool specifiedInstance =
     (
         !overwrite
-     && args.optionReadIfPresent("resultTime", meshInstance)
+     && args.readIfPresent("resultTime", meshInstance)
     );
 
     if (specifiedInstance)