Update adafruit_avrprog.py

Added support for Record type 4, as described here:
https://en.wikipedia.org/wiki/Intel_HEX#Record_types

Author: mafiltenborg

adafruit_avrprog.py

@@ -420,6 +420,10 @@ def read_hex_page(file_state, page_addr, page_size, page_buffer):
             continue
         if rec_type == 3:  # sometimes appears, we ignore this
             continue
+        if rec_type == 4:
+            file_state["ext_addr"] = int(line[9:13], 16) << 16
+            #print("ExtLin addr: %05X" % file_state['ext_addr'])
+            continue
         if rec_type != 0:  # if not the above or a data record...
             raise RuntimeError(
                 "Unsupported record type %d on line %d" % (rec_type, file_state["line"])