read evidence metadata from JGF
read evidence metadata from JGF

reads evidence.metadata.document_header from graph id/label

reads evidence.metadata.annotation_definitions from graph metadata

reads evidence.metadata.namespace_definitions from graph metadata

provides default resource index option for deserialize if not specified
in graph metadata (defaults to 20131211 resource index if not provided).

refs #45

abargnesi/bel.rb,nbargnesi/bel.rb,OpenBEL/bel.rb,abargnesi/bel.rb,abargnesi/bel.rb,abargnesi/bel.rb,OpenBEL/bel.rb,OpenBEL/bel.rb,nbargnesi/bel.rb,abargnesi/bel.rb,nbargnesi/bel.rb,nbargnesi/bel.rb,OpenBEL/bel.rb,nbargnesi/bel.rb,abargnesi/bel.rb,OpenBEL/bel.rb,OpenBEL/bel.rb,nbargnesi/bel.rb,OpenBEL/bel.rb