apply fixes to metadata
apply fixes to metadata

This extends the logic that forces the data in the class to look a
certain way. Like the top-level elements of values, it does a to_sym on
:document_header. If :bel_version is not supplied, the latest supported
version is assumed. Authors and Licenses are coerced into arrays if
necessary. And == is provided.

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