Reduce patch applying cost.

Let the developer to decide does he wants to modify same object or copy of it. In other way test operation produces huge overhead for nothing.

jsonpatch.py

@@ -39,7 +39,6 @@ __website__ = 'https://github.com/stefankoegl/python-json-patch'
 __license__ = 'Modified BSD License'
 
 
-import copy
 import json
 
 
@@ -85,9 +84,7 @@ class JsonPatch(object):
 
 
     def apply(self, obj):
-        """ Applies the patch to a copy of the given object """
-
-        obj = copy.deepcopy(obj)
+        """ Applies the patch to given object """
 
         for operation in self.patch:
             op = self._get_operation(operation)