ENH: add refPtr release() method

- releases ownership of the pointer. A no-op (and returns nullptr)
  for references.

  Naming consistent with unique_ptr and autoPtr.

DOC: adjust wording for memory-related classes

- add is_const() method for tmp, refPtr.

  Drop (ununsed and confusing looking) isTmp method from refPtr
  in favour of is_pointer() or movable() checks

ENH: noexcept for some pTraits methods, remove redundant 'inline'

- test for const first for tmp/refPtr (simpler logic)

applications/test/sizeof/Test-sizeof.C

@@ -39,6 +39,7 @@ Description
 #include "argList.H"
 #include "Time.H"
 #include "IOobject.H"
+#include "scalarField.H"
 
 namespace Foam
 {
@@ -139,6 +140,8 @@ int main(int argc, char *argv[])
     cout<<"PstreamBuffers:" << sizeof(Foam::PstreamBuffers) << nl;
     cout<<"Time:" << sizeof(Foam::Time) << nl;
 
+    cout<<"tmp<>:" << sizeof(tmp<scalarField>) << nl;
+
     Info << "---\nEnd\n" << endl;
 
     return 0;