modified getMessages() to return an object instead of an array

the object contains the messages per validation name. this makes
it possible to render messages where they belong to (ie. the input
fields whose value didn't validate).
getMessages() returns empty message arrays for successful validations
instead of omitting them.

this makes it easier to loop over messages in templates (ie. no need to
check if a property is set before rendering the messages)

updated documentation/examples
Merge pull request #6 from grob/getmessages

modified getMessages() to return an object instead of an array :shipit: