ENH: functionObjects: refactor and extend histogram

- new submodels:
  - 'equalBinWidth': groups data into bins of equal widths (previous behaviour)
  - 'unequalBinWidth': groups data into bins of unequal widths

- output files per time-step are replaced with a single output file

- silently deprecates the input entries: 'setFormat' and 'formatOptions'

tutorials/incompressible/pisoFoam/RAS/cavity/system/FOs/FOhistogram

@@ -12,15 +12,54 @@ histogram1
     type            histogram;
     libs            (fieldFunctionObjects);
     field           p;
-    nBins           100;
-    setFormat       raw;
+    model           equalBinWidth;
 
-    // Optional entries
+    // Conditional entries
+    nBins           100;
     max             10;
     min            -10;
 
-    // Optional (inherited) entries
-    writePrecision   16;
+    // Inherited entries
+    writePrecision   6;
+    writeToFile      true;
+    useUserTime      true;
+
+    region          region0;
+    enabled         true;
+    log             true;
+    timeStart       0;
+    timeEnd         1000;
+    executeControl  timeStep;
+    executeInterval 1;
+    writeControl    writeTime;
+    writeInterval   -1;
+}
+
+
+histogram2
+{
+    // Mandatory entries
+    type            histogram;
+    libs            (fieldFunctionObjects);
+    field           p;
+    model           unequalBinWidth;
+
+    // Conditional entries
+    ranges
+    (
+        // min  max
+        (-10    -9)    // bin-0
+        (-9     -8)    // bin-1
+        (-8     -7)
+        (-7     -6)
+        (-6     -2)
+        (-2      0)
+        (0       5)
+        (5       10)
+    );
+
+    // Inherited entries
+    writePrecision   6;
     writeToFile      true;
     useUserTime      true;