add roundness/aspect jitter

src/brush.h

@@ -51,6 +51,8 @@ public:
     float m_jitter_hue = 0;
     float m_jitter_sat = 0;
     float m_jitter_val = 0;
+    float m_jitter_aspect = 0;
+    bool  m_jitter_aspect_bothaxis = false;
     int   m_blend_mode = 0;
 
     bool  m_tip_invert = false;