Override dict.copy method on AttributeDict

The copy implementation of dict always returns a dict instead of copying the
current dict subclass.

Author: GraylinKim

sc2reader/utils.py

@@ -497,6 +497,9 @@ def __getattr__(self, name):
     def __setattr__(self, name, value):
         self[name] = value
 
+    def copy(self):
+        return AttributeDict(super(AttributeDict,self).copy())
+
 def read_header(file):
     ''' Read the file as a byte stream according to the documentation found at:
             http://wiki.devklog.net/index.php?title=The_MoPaQ_Archive_Format