Make all array constructors explicit (#99)

* Make all array constructors explicit

to avoid accidental implicit casts like e.g.
Vector3f v = 0;
assigning nullpointer content.

matrix/SquareMatrix.hpp

@@ -28,7 +28,12 @@ class SquareMatrix : public Matrix<Type, M, M>
 public:
     SquareMatrix() = default;
 
-    SquareMatrix(const Type data_[M][M]) :
+    explicit SquareMatrix(const Type data_[M][M]) :
+        Matrix<Type, M, M>(data_)
+    {
+    }
+
+    explicit SquareMatrix(const Type data_[M*M]) :
         Matrix<Type, M, M>(data_)
     {
     }