LoxiGen: start generating pyloxi 1.3

Not all classes are fully implemented.
pyloxi: generate OXM classes
pyloxi: implement of_ipv6_t
LoxiGen: add OF 1.3 OF_HELLO_ELEM_TYPE group
pyloxi: support hello_elems
Merge branch 'master' into pyloxi-1.3

Also added ofp_hello_elem_type to standard-1.3.

Conflicts:
	loxi_front_end/translation.py
Merge pull request #2 from rlane/pyloxi-1.3

Initial PyLoxi 1.3 work