feat: support graphic connector

The rendering material is automatically generated. You don't need to pre-generate the material.
The generated materials are cached and properly batched.

Close #75, #76, #80

BREAKING CHANGE: The name of the custom SoftMaskable shader should be `<ShaderName> (SoftMaskable)`. For more information, see the "Support soft masks with your custom shaders" section of the README.

Packages/SoftMaskForUGUI/Samples/Demo/SoftMask_Demo.cs

@@ -10,11 +10,14 @@ public class SoftMask_Demo : MonoBehaviour
 		[SerializeField] RawImage[] softMaskBufferViewer;
 		[SerializeField] SoftMask[] softMask;
 		[SerializeField] Text text;
+		[SerializeField] GameObject title;
 
 
 		// Use this for initialization
 		void OnEnable()
 		{
+			title.SetActive(true);
+
 			text.text = string.Format("GPU: {0}\nDeviceType: {1}\nShaderLevel: {2}\nUVStartsAtTop: {3}",
                 SystemInfo.graphicsDeviceName,
                 SystemInfo.graphicsDeviceType,
@@ -25,13 +28,6 @@ void OnEnable()
 			{
 				softMaskBufferViewer[i].texture = softMask[i].softMaskBuffer;
 			}
-
-		}
-
-		// Update is called once per frame
-		void Update()
-		{
-
 		}
 
 		public void SetWorldSpase(bool flag)
@@ -60,4 +56,4 @@ public void SetOverlay (bool flag)
 			}
 		}
 	}
-}
+}