Math: added utility function Vector2::aspectRatio().

Consider this craziness when setting up projection or something similar:

    Vector2i framebufferSize;
    Float aspectRatio = Float(framebufferSize.x())/framebufferSize.y();

And now, behold, the convenience:

    Float aspectRatio = Vector2(framebufferSize).aspectRatio();

src/Math/Test/Vector2Test.cpp

@@ -67,6 +67,7 @@ class Vector2Test: public Corrade::TestSuite::Tester {
         void axes();
         void scales();
         void perpendicular();
+        void aspectRatio();
 
         void debug();
         void configuration();
@@ -90,6 +91,7 @@ Vector2Test::Vector2Test() {
               &Vector2Test::axes,
               &Vector2Test::scales,
               &Vector2Test::perpendicular,
+              &Vector2Test::aspectRatio,
 
               &Vector2Test::debug,
               &Vector2Test::configuration});
@@ -196,6 +198,11 @@ void Vector2Test::perpendicular() {
     CORRADE_COMPARE(Vector2::xAxis().perpendicular(), Vector2::yAxis());
 }
 
+void Vector2Test::aspectRatio() {
+    const Vector2 a(3.0f, 4.0f);
+    CORRADE_COMPARE(a.aspectRatio(), 0.75f);
+}
+
 void Vector2Test::debug() {
     std::ostringstream o;
     Debug(&o) << Vector2(0.5f, 15.0f);

src/Math/Vector2.h

@@ -134,6 +134,15 @@ template<class T> class Vector2: public Vector<2, T> {
          */
         Vector2<T> perpendicular() const { return {-y(), x()}; }
 
+        /**
+         * @brief Aspect ratio
+         *
+         * Returns quotient of the two elements. @f[
+         *      a = \frac{v_x}{v_y}
+         * @f]
+         */
+        T aspectRatio() const { return x()/y(); }
+
         MAGNUM_VECTOR_SUBCLASS_IMPLEMENTATION(2, Vector2)
 };