Fix typo in readme
Fix logging.debug(..) -> log.debug(..)
Remove old comment with dead link
Merge pull request #85 from Treora/edits

Some minor edits
First attempt at using Open Annotation Data Model

Annotations can now be serialised into JSON-LD formatted RDF, following
the data model spec: http://www.openannotation.org/spec/core/
Use OrderedDict for OA representation

Because JSON-LD spec recommends keeping @context at the top.
Better checks for absent fields in creating jsonld
Fall back to dict if OrderedDict unavailable
Code reordering and renaming
Small edits&fixes
Use OA context from w3.org
Set jsonld_baseurl default to None
Semantify user

Let's keep the default very generic, for example we don't even know if
users are Persons. Implementors can subclass Annotation to add more user
info (as with any of the properties).