new function: get_vid_bytes(). returns VID bytes from valid MAC address,

thows type error if address is incorrect

Author: NetworkJack2

README.md

@@ -70,3 +70,9 @@ Check if a MAC address is valid
 if g.is_mac_address('94:0C:98:BC:74:1C') == True:
     print('Valid Ethernet Address')
 ```
+
+Get the VID bytes from a MAC address
+```
+g.get_vid_bytes('94:0C:98:BC:74:1C')
+'94:0C:98'
+```

generate_mac/__init__.py

@@ -207,3 +207,16 @@ def is_mac_address(mac_address):
             return True
         else:
             return False
+    
+    def get_vid_bytes(mac_address):
+        '''return vendor bytes from a given MAC address as a string'''
+        # check if this is a valid mac address
+        if generate_mac.is_mac_address(mac_address) != True:
+            raise ValueError(mac_address + ' is not a validi MAC address')
+
+        output = ""
+        # Grab the first three bytes, this is the VID
+        mac_bytes = mac_address.split(":")
+        output = ":".join(mac_bytes[0:3])
+
+        return output