Added Jenkin's hash functions in C++ form

- not much speed difference between SuperFastHash and Jenkin's lookup3 but
  both are 5-10% faster than what is currently implemented in Foam::string,
  albeit inlining probably helps there.

- TODO: integration with existing infrastructure

applications/test/Hashing/hashingTests

@@ -0,0 +1,40 @@
+/*-------------------------------*- C++ -*---------------------------------*\
+|    =========                                                              |
+|    \\      /     OpenFOAM                                                 |
+|     \\    /                                                               |
+|      \\  /       The Open Source CFD Toolbox                              |
+|       \\/                                        http://www.OpenFOAM.org  |
+\*-------------------------------------------------------------------------*/
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+stringList
+(
+    "The quick brown fox jumps over the lazy dog"
+    "The best hash is the one you don't write yourself!"
+)
+
+
+labelList
+(
+    0
+    1
+    100
+    1000
+    -1
+    -10
+    -100
+)
+
+labelListList
+(
+    (0)
+    (0 0)
+    (0 0 0)
+    (0 1)
+    (100 1000)
+    (0 1 100 1000)
+)
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //