Experimental 'jsonld.objectify' to link flattened graph in-memory

Corrected recursion bug:  follow the top-level flattened subject!

(Precious behavior was recursing down the already-replaced branches
instead of tracking the replacement.)

Updated err message
Fix blank node check in _flatten.
Handle named graphs in flatten.
Handle @type blank node IRIs.
Clean up/simplify flatten.
Fix @list merging bug.
Minor doc fix.
Add RDF parser for RDFa API data object.
Fix bugs with XML literals.
Only define XMLSerializer if needed.
Add first pass of package.json.
A few jshint cleanups.

- odd ! usage
- unneeded ;
- missing var
Update to fix value compaction when there is a default language.
Fix nquads output for graph w/bnode ID.
Use available aliases for @value, @language when compacting.
Change addValue to allow duplicates by default.
Remove duplicate RDF statements.
Fix list term check.
Remove bad dependencies.
Add check for undefined elements during expansion.