First changes for Python3 support

A lot of errors are now gone when using test.py.
However I don't know how to solve these two issues : 

ERROR: test_rule_address (iptc.test.test_iptc.TestRule6)
Traceback (most recent call last):
  File "/home/Fr3ya/python-iptables/iptc/test/test_iptc.py", line 380, in test_rule_address
    rule.src = addr
  File "/home/Fr3ya/python-iptables/iptc/ip6tc.py", line 340, in set_src
    self._create_mask(plen))
TypeError: expected an object with a buffer interface

and this one : 

ERROR: test_rule_insert (iptc.test.test_iptc.TestRule6)
Traceback (most recent call last):
  File "/home/Fr3ya/python-iptables/iptc/test/test_iptc.py", line 526, in test_rule_insert
    target = iptc.Target(rule, "ACCEPT")
  File "/home/Fr3ya/python-iptables/iptc/ip4tc.py", line 610, in __init__
    raise XTablesError("can't find target %s" % (name))
iptc.xtables.XTablesError: can't find target ACCEPT