DOC: elaborate the usage of function objects

ENH: update libs of etc/caseDicts/postProcess items
  ENH: ensure destructor=default
  ENH: ensure constness
  ENH: ensure no 'copy construct' and 'no copy assignment' exist
  TUT: add examples of function objects with full set
       of settings into a TUT if unavailable
  TUT: update pisoFoam/RAS/cavity tutorial in terms of usage

src/functionObjects/field/MachNo/MachNo.C

@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2016 OpenFOAM Foundation
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2020 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -37,13 +37,7 @@ namespace Foam
 namespace functionObjects
 {
     defineTypeNameAndDebug(MachNo, 0);
-
-    addToRunTimeSelectionTable
-    (
-        functionObject,
-        MachNo,
-        dictionary
-    );
+    addToRunTimeSelectionTable(functionObject, MachNo, dictionary);
 }
 }
 
@@ -89,10 +83,4 @@ Foam::functionObjects::MachNo::MachNo
 }
 
 
-// * * * * * * * * * * * * * * * * Destructor  * * * * * * * * * * * * * * * //
-
-Foam::functionObjects::MachNo::~MachNo()
-{}
-
-
 // ************************************************************************* //

src/functionObjects/field/MachNo/MachNo.H

@@ -6,6 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2016 OpenFOAM Foundation
+    Copyright (C) 2020 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -30,11 +31,51 @@ Group
     grpFieldFunctionObjects
 
 Description
-    Calculates and writes the Mach number as a volScalarField.
+    Computes the Mach number as a \c volScalarField.
+
+    Operands:
+    \table
+      Operand          | Type           | Location
+      input            | volVectorField | $FOAM_CASE/<time>/<inpField>
+      output file      | -              | -
+      output field     | volScalarField | $FOAM_CASE/<time>/<outField>
+    \endtable
+
+Usage
+    Minimal example by using \c system/controlDict.functions:
+    \verbatim
+    MachNo1
+    {
+        // Mandatory entries (unmodifiable)
+        type            MachNo;
+        libs            (fieldFunctionObjects);
+
+        // Optional (inherited) entries
+        ...
+    }
+    \endverbatim
+
+    where the entries mean:
+    \table
+      Property     | Description                        | Type | Req'd | Dflt
+      type         | Type name: MachNo                  | word |  yes  | -
+      libs         | Library name: fieldFunctionObjects | word |  yes  | -
+    \endtable
+
+    The inherited entries are elaborated in:
+     - \link functionObject.H \endlink
+     - \link fieldExpression.H \endlink
+
+    Minimal example by using the \c postProcess utility:
+    \verbatim
+        postProcess -func MachNo
+    \endverbatim
 
 See also
-    Foam::functionObjects::fieldExpression
-    Foam::functionObjects::fvMeshFunctionObject
+    - Foam::functionObject
+    - Foam::functionObjects::fvMeshFunctionObject
+    - Foam::functionObjects::fieldExpression
+    - ExtendedCodeGuide::functionObjects::field::MachNo
 
 SourceFiles
     MachNo.C
@@ -84,9 +125,15 @@ public:
             const dictionary& dict
         );
 
+        //- No copy construct
+        MachNo(const MachNo&) = delete;
+
+        //- No copy assignment
+        void operator=(const MachNo&) = delete;
+
 
     //- Destructor
-    virtual ~MachNo();
+    virtual ~MachNo() = default;
 };