Apply skew using Surface::transform

The Surface interface does not define a skewX nor a skewY method. For the time being we can achieve the same result using a generic transformation matrix.

Author: bsweeney

src/Svg/Tag/AbstractTag.php

@@ -176,11 +176,13 @@ protected function applyTransform($attributes)
                         break;
 
                     case "skewX":
-                        $surface->skewX($t[1]);
+                        $tan_x = tan(deg2rad($t[1]));
+                        $surface->transform(1, 0, $tan_x, 1, 0, 0);
                         break;
 
                     case "skewY":
-                        $surface->skewY($t[1]);
+                        $tan_y = tan(deg2rad($t[1]));
+                        $surface->transform(1, $tan_y, 0, 1, 0, 0);
                         break;
                 }
             }