Merge pull request #25 from jhalterman/master

Updated readme to describe vert.igo google group.
Refactor core serializer to load serializers by type, allowing for providing type-specific custom serializers.
Create a fixed heartbeat interval.
Refactor serialization API to use typed/named serializers.
Refactor networks API to use polymorphism for providing module/verticle deployment options.
Clean up network API documentation.
Move Input to network package for consistency by extending the deprecated Input class.
Refactor context API to use polymorphism for module/verticle configurations.
Add input contexts to context API.
Add documentation for input configuration fields.
Add basic network unit tests.
Add unit tests for creating networks from json.
Add network from json unit tests.
Deprecate the Component.fromJson() method.
Add extensive network context unit tests.
Always use component numInstances() in input counts.
Ensure input IDs are properly added to inputs when constructed from JSON.
Support disabling timeouts in network auditors.
Support deploying components as worker verticles.
Do not allow modules to be constructed with invalid module identifiers.