HashTable: Added C++11 initializer_list constructor

e.g.
    HashTable<label, string> table1
    {
        {"kjhk", 10},
        {"kjhk2", 12}
    };

    HashTable<label, label, Hash<label>> table2
    {
        {3, 10},
        {5, 12},
        {7, 16}
    };

src/OpenFOAM/containers/HashTables/HashTable/HashTable.H

@@ -49,6 +49,7 @@ SourceFiles
 #include "word.H"
 #include "Xfer.H"
 #include "className.H"
+#include <initializer_list>
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
@@ -62,6 +63,9 @@ template<class T> class UList;
 template<class T, class Key, class Hash> class HashTable;
 template<class T, class Key, class Hash> class HashPtrTable;
 
+template<class Type1, class Type2>
+class Tuple2;
+
 template<class T, class Key, class Hash>
 Istream& operator>>(Istream&, HashTable<T, Key, Hash>&);
 
@@ -171,6 +175,7 @@ class HashTable
         //- Assign a new hashedEntry to a possibly already existing key
         bool set(const Key&, const T& newElmt, bool protect);
 
+
 public:
 
     // Forward declaration of iterators
@@ -207,6 +212,9 @@ public:
         //- Construct by transferring the parameter contents
         HashTable(const Xfer<HashTable<T, Key, Hash>>&);
 
+        //- Construct from an initializer list
+        HashTable(std::initializer_list<Tuple2<Key, T>> lst);
+
 
     //- Destructor
     ~HashTable();