Bugs: network formats (0.28.1) #36

Defects in the network-format value objects of 0.28.1 (security/ipv4.py, ipv6.py, mac_address.py, email_address.py, url.py; each one reproduced). Fixed by the new network.py family; every item gets a regression test and is ticked when the fix lands.

• C25 Ipv4 accepts octets with leading zeros ('01.02.03.004', ambiguous octal notation), unlike the stdlib ipaddress.
• C26 Ipv6 regex has false positives (malformed fe80 zone forms, leading-zero embedded IPv4) and false negatives (zone IDs, full-form embedded IPv4, upper-case ::FFFF:).
• C27 EmailAddress accepts malformed dot/hyphen placements ('a..b@example.com') and rejects common valid local parts and IDN (xn--) TLDs.
• X07 EmailAddress enforces no RFC length limits (local part > 64, DNS label > 63, address > 254 are accepted).
• C28 Url accepts invalid hosts/ports and scheme-less strings, and rejects valid URLs with fragments, userinfo or IPv6 hosts.
• X01 Url accepts non-ASCII look-alike letters in the host (Kelvin sign, dotless i, long s) through re.IGNORECASE.
• C31 MacAddress accepts mixed separators within one address ('00:1A-2B:3C-4D:5E').