add write_cgram function

Author: shaoziyang

lcd/I2C_LCD1602/i2c_lcd1602.py

@@ -60,6 +60,12 @@ def autoaddr(self):
                 pass
         raise Exception('I2C address detect error!')
 
+    def write_cgram(self, buf, reg=0):
+        n = len(buf)
+        self.setcmd(0x40 + (reg%8)*8)
+        for i in range(n):
+            self.setdat(buf[i])
+
     def clear(self):
         self.setcmd(1)