Remove appbase as an external dependency.

lib/appbase/util/Clamp.hpp

@@ -0,0 +1,13 @@
+#pragma once
+
+namespace AB_NAMESPACE {
+
+// http://en.cppreference.com/w/cpp/algorithm/clamp
+
+template <class T>
+constexpr const T &clamp(const T &v, const T &lo, const T &hi)
+{
+    return assert(!(hi < lo)), (v < lo) ? lo : (hi < v) ? hi : v;
+}
+
+}  // namespace AB_NAMESPACE