Add I2C General Call Commands

This Commit, 
- Adds _general_call static methods for executing different general calls to MCP4728
- Adds reset, wakeup and soft_update general call static methods

Author: codenio

adafruit_mcp4728.py

@@ -36,6 +36,7 @@
 
 _MCP4728_CH_A_MULTI_EEPROM = 0x50
 
+_MCP4728_GENERAL_CALL_ADDRESS = 0x00
 
 class CV:
     """struct helper"""
@@ -227,6 +228,41 @@ def _chunk(big_list, chunk_size):
         for i in range(0, len(big_list), chunk_size):
             yield big_list[i : i + chunk_size]
 
+    @staticmethod
+    def _general_call(byte_command):
+        buffer_list = [_MCP4728_GENERAL_CALL_ADDRESS]
+        buffer_list += byte_command
+
+        buf = bytearray(buffer_list)
+
+        with self.i2c_device as i2c:
+            i2c.write(buf)
+
+    @staticmethod
+    def reset():
+        """Internal Reset similar to a Power-on Reset (POR).
+        The contents of the EEPROM are loaded into each DAC input
+        and output registers immediately"""
+
+        reset_command = [0x06]
+        self._general_call(reset_command)
+
+    @staticmethod
+    def wakeup():
+        """Reset the Power-Down bits (PD1, PD0 = 0,0) and
+        Resumes Normal Operation mode"""
+
+        wakeup_command = [0x09]
+        self._general_call(wakeup_command)
+
+    @staticmethod
+    def soft_update():
+        """Updates all DAC analog outputs (VOUT) at the same time."""
+
+        soft_update_command = [0x08]
+        self._general_call(soft_update_command)
+
+    #TODO : general_call read address
 
 class Channel:
     """An instance of a single channel for a multi-channel DAC.