Force bin json (#2456)

* Fix bug where small values of max_bin cause crash.

* Revert "Fix bug where small values of max_bin cause crash."

This reverts commit fe5c8e2547057c1fa5750bcddd359dd7708fab4b.

* Add json files for forced bin example.

* Add second json file.

examples/regression/forced_bins.json

+[
+    {
+        "feature": 0,
+        "bin_upper_bound": [ 0.3, 0.35, 0.4 ]
+    },
+    {
+        "feature": 1,
+        "bin_upper_bound": [ -0.1, -0.15, -0.2 ]
+    }
+]

examples/regression/forced_bins2.json

+[
+    {
+        "feature": 0,
+        "bin_upper_bound": [ 0.19, 0.39, 0.59, 0.79 ]
+    }
+]