Add cpp clamp function to util.h, switched battery and signal strength percentage calcs to it #197

src/utils.h

@@ -0,0 +1,7 @@
+#pragma once
+
+/// C++ v17+ clamp function, limits a given value to a range defined by lo and hi
+template<class T>
+constexpr const T& clamp( const T& v, const T& lo, const T& hi ) {
+    return (v < lo) ? lo : (hi < v) ? hi : v;
+}