Rename "type" to "field" in OXM field lists.
Add YAML unit test for MatchBuilder.
Change instruction 'type' to 'instruction'.

- Move instruction parameters up a level (not a dict under value).
OFPAT_SET_FIELD takes a 'field' attribute, not 'type'.
Add output support for YAML IteratorMethodTraits.

Use iterator for SequenceTraits implementation for Match.
Replace more Range YAML SequenceTraits with iterators.