Implement browsing functionality

[millar]

At the moment documents can only be managed in a singular fashion.

Would be nice to have search/filtration/ordering of documents to find their IDs if unknown.

Potential API:

api = Api()

documents = api.documents.where(name='name').order_by('-created_at')
# => return a document manager where each document is a api.document.set(id)
#    from the results of the API call
# Could also pre-install metadata from the initial query to reduce future calls

for document in documents:
    print document.id