Several updates and bug fixes:

- Now keeps <metadata> node serialized (character text not permitted,
  but arbitrary XML structure is, so we maintain this convention).
- Fixed parsing of associatedParty, added it's additional attribute
  (role)
- Fixed parsing of keywords (before keywords were blank, since
  keywordSet had child nodes that were both keyword and
  keywordThesarurus.  Also fixed the keyword extraction method.
  This required edites to emlToS4 routine.
- Fixed S4Toeml routine to properly avoid including ecluded_slots,
  such as `dirname`, which was getting written out to the physical node
- Working out several minor changes to access methods.
- added show as yaml methods for coverage child nodes.
- updated documentation