v3.0.0 - Major update with event reformatting and event tracking

Breaking changes:

• feat: removed intermediate Avro types from event payload (#9).
  For example: { city : { string: 'SFO' } } becomes { city: 'SFO' }.

Changes:

• feat: new event tracking and lifecycle event (partly addresses #12).
  • Subscribe methods now return a PubSubEventEmitter that inherits from EventEmitter (no signature change). PubSubEventEmitter exposes methods that tracks the topic name, the number of requested events and the number of received events.
  • The client now automatically fires a lastevent event via PubSubEventEmitter when we have reached number of requested event.