Add the ability to close splits and change splits using the mouse

This commits adds split navigation with the mouse and the ability to
close splits. You can now also open a file directly with the hsplit
and vsplit commands.

cmd/micro/micro.go

@@ -281,11 +281,17 @@ func main() {
 		case *tcell.EventMouse:
 			if e.Buttons() == tcell.Button1 {
 				_, h := screen.Size()
-				_, y := e.Position()
+				x, y := e.Position()
 				if y == h-1 && messenger.message != "" {
 					clipboard.WriteAll(messenger.message)
 					continue
 				}
+
+				for _, v := range tabs[curTab].views {
+					if x >= v.x && x < v.x+v.width && y >= v.y && y < v.y+v.height {
+						tabs[curTab].curView = v.Num
+					}
+				}
 			}
 		}