support _bulk_docs properties

the couchdb wiki defines the 2 types below:

all_or_nothing (boolean)
new_edits (boolean)

http://wiki.apache.org/couchdb/HTTP_Bulk_Document_API#Transactional_Semantics_with_Bulk_Updates
let JSON allow_nonref encoding()

it will do the right thing for integers and nulls
Merge pull request #8 from c0decafe/master

some enhancements