Documentation clarification, assertion update.

Don't yell at the user all the time.

src/Math/Test/VectorTest.cpp

@@ -110,7 +110,7 @@ void VectorTest::angle() {
     Error::setOutput(&o);
     /* Both vectors must be normalized, otherwise NaN is returned */
     CORRADE_COMPARE(Vector3::angle(Vector3(2.0f, 3.0f, 4.0f).normalized(), {1.0f, -2.0f, 3.0f}), numeric_limits<Vector3::Type>::quiet_NaN());
-    CORRADE_COMPARE(o.str(), "Math::Vector::angle(): vectors must be normalized!\n");
+    CORRADE_COMPARE(o.str(), "Math::Vector::angle(): vectors must be normalized\n");
     CORRADE_COMPARE(Vector3::angle({2.0f, 3.0f, 4.0f}, Vector3(1.0f, -2.0f, 3.0f).normalized()), numeric_limits<Vector3::Type>::quiet_NaN());
 
     CORRADE_COMPARE(Vector3::angle(Vector3(2.0f, 3.0f, 4.0f).normalized(), Vector3(1.0f, -2.0f, 3.0f).normalized()), rad(1.162514f));

src/Math/Vector.h

@@ -85,12 +85,12 @@ template<size_t s, class T> class Vector: public RectangularMatrix<1, s, T> {
          * @f[
          * \phi = \frac{a \cdot b}{|a| \cdot |b|}
          * @f]
-         * @attention If any of the parameters is not normalized (and
-         * assertions are enabled), returns NaN.
+         * @attention Assertion fails on non-normalized vectors and NaN is
+         *      returned.
          */
         inline static T angle(const Vector<size, T>& a, const Vector<size, T>& b) {
             CORRADE_ASSERT(MathTypeTraits<T>::equals(a.dot(), T(1)) && MathTypeTraits<T>::equals(b.dot(), T(1)),
-                           "Math::Vector::angle(): vectors must be normalized!", std::numeric_limits<T>::quiet_NaN());
+                           "Math::Vector::angle(): vectors must be normalized", std::numeric_limits<T>::quiet_NaN());
             return std::acos(dot(a, b));
         }