Math: added Range::data().

The main side-effect of this is that the data layout is now really
specified, making it useful for various glGet*(GL_*_RANGE) calls.

src/Magnum/Math/Range.h

@@ -103,6 +103,13 @@ template<UnsignedInt dimensions, class T> class Range {
             return !operator==(other);
         }
 
+        /**
+         * @brief Raw data
+         * @return One-dimensional array of `dimensions`*2 length.
+         */
+        T* data() { return _min.data(); }
+        constexpr const T* data() const { return _min.data(); } /**< @overload */
+
         /**
          * @brief Minimal coordinates (inclusive)
          *