Add FreeBitmap and Update docs

docs/doc.md

@@ -46,6 +46,7 @@
 ##### [TostringBitmap](#TostringBitmap)
 ##### [GetPortion](#GetPortion)
 ##### [Convert](#Convert)
+#### [FreeBitmap](#FreeBitmap)
 
 ## [Event](#Event)
 
@@ -398,6 +399,20 @@ robotgo.ScrollMouse(50, "down")
 robotgo.Convert("test.png", "test.tif")
 ```             
 
+### <h3 id="FreeBitmap">.FreeBitmap(MMImageType)</h3>
+
+    FreeBitmap free and dealloc bitmap
+
+#### Arguments:
+
+    MMImageType
+
+#### Examples:
+
+```Go
+robotgo.FreeBitmap(bitmap)
+```    
+
 ## <h2 id="Event">Event</h2> 
 
 ### <h3 id="AddEvent">.AddEvent(string)</h3>

docs/doc_zh.md

@@ -49,6 +49,7 @@
 ##### [TostringBitmap](#TostringBitmap)
 ##### [GetPortion](#GetPortion)
 ##### [Convert](#Convert)
+#### [FreeBitmap](#FreeBitmap)
 
 ## [事件](#Event)
 
@@ -413,6 +414,20 @@ robotgo.ScrollMouse(50, "down")
 ```Go
 robotgo.Convert("test.png", "test.tif")
 ```  
+
+### <h3 id="FreeBitmap">.FreeBitmap(MMImageType)</h3>
+
+    FreeBitmap free and dealloc bitmap
+
+#### 参数:
+
+    MMImageType
+
+#### 示例:
+
+```Go
+robotgo.FreeBitmap(bitmap)
+```    
 ## <h2 id="Event">事件</h2> 
 
 ### <h3 id="AddEvent">.AddEvent(string)</h3>

robotgo.go

@@ -639,6 +639,11 @@ func Convert(args ...interface{}) {
 	SaveBitmap(bitmap, spath, mtype)
 }
 
+// FreeBitmap free and dealloc bitmap
+func FreeBitmap(ref C.MMBitmapRef) {
+	C.destroyMMBitmap(ref)
+}
+
 /*
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