Start work on 0.6 release
Provide access to objects name/id

Server.db('dbname') => Database.name => 'dbname'
Database.doc('docid') => Document.id => 'docid'
Document.att('attname') => Attachment.name => 'attname'
Database.ddoc('ddoc') => DesignDocument.id => '_design/ddoc'
Database.ddoc('ddoc') => DesignDocument.name => 'ddoc'
Fix check for aiohttp.request function call
Construct Database/Document/Attachment via __getitem__ protocol

Instead:

    db = yield from server.db('mydb')
    info = yield from db.info()

Use:

    db = server['mydb']
    info = yield from db.info()

Whenever you don't need to check if you have access permission to
the specified object. This method saves one HEAD request for you, but
doesn't ensures you that target object is welcome to work with you.

Same trick is true for documents and attachments:

    att = server['mydb']['_design/ddoc']['index.html']

Design documents will be handled with care and correct interface would
be returned back if docid contains '_design/' prefix.
Prefer short named db/doc/ddoc/att constructors

Never found myself using long version and keeping one way to do a thing
is better.
Add helper to get current document's revision
Cover doesn't need in test argument
Fix docstring