of-wire json test: unit test
stringify.StringifyMixin.__str__: simplify

simplify the code a bit.
suggested by Isaku Yamahata.
no functional changes are intended.
ofproto: generate OFPXMT_OFB_ and OXM_OF_ from a single source
binary <-> text conversion of mac/ipv4/ipv6 addresses

implemented as a simple wrapper of netaddr.

background:
    the goal is to use the consistent representations of addresses
    throughout the tree, instead of the current ad-hoc representations
    like a list of int16 for ipv6 address.

    - netaddr style text (eg. '10.0.0.1', 'ff02::1') for ryu-app level api.
    - on-wire binary for internal use.

    this is the first step to the direction.  ie. have a single
    implementation of address representation conversion.
replace homegrown bin<->text routines with addrconv for mac and ipv6
use bytes instead of int to represent ipv4 addresses

change ipv4 representation from int to bytes in many places.
replace homegrown bin<->text routines with addrconv for ipv4.
oxm_fields: add conversion routines
of13: new OFPMatch composer api

a new api to compose matches.  it looks like:

    match = OFPMatch(in_port=1,
                     eth_type=0x86dd,
                     ipv6_src=('2001:db8:bd05:1d2:288a:1fc0:1:10ee',
                               'ffff:ffff:ffff:ffff::'),
                     ipv6_dst = '2001:db8:bd05:1d2:288a:1fc0:1:10ee')

the old match.set_foo and match.append_field methods are kept for now
but will be removed later.
oxm_fields: make this a little non-OFPXMC_OPENFLOW_BASIC friendly
of13: new match field parser

add a new match field parser which fills OFPMatch attributes used
by the new api.

the old parser which fills match.fields is kept for now but will be
removed later.
of13: make OFPMatch support some dict-like ops

an example:

    if 'ipv6_src' in match:
        print match['ipv6_src']
of12: new OFPMatch composer api
of12: new match field parser
of12: make OFPMatch support some dict-like ops
oxm_fields: optimize field lookup

as suggested by yamahata-san
add oxm_fields.normalize_user
of13: use oxm_fields.normalize_user
of13: use list comprehension

as yamahata-san suggested
oxm_fields: comment
of12: use oxm_fields.normalize_user