Snowplow Ruby Tracker v0.2.0

Bringing the Ruby Tracker up to date with the other Snowplow trackers, particularly around support of self-describing custom contexts and unstructured events.

• Blog post

API updates

• Wrapped custom contexts in the contexts schema, thanks @ebear! (#25)
• Wrapped unstructured event payload in the unstructured_event schema, thanks @ebear! (#22)
• Removed event name and vendors as argument to track_unstruct_event, thanks @ebear! (#19)
• Removed event vendor and context vendor from the payload (#35)

Under the hood

• Now generates UUID for event_id and sends as eid parameter (#29)
• No longer setting and sending tid (#30)
• Created new contracts for unstructured events and custom contexts (#34)
• Updated track_screen_view to send valid self-describing screen_view JSON, thanks @ebear! (#21)

Documentation and testing

• Fixed Snowplow capitalization (#28)
• Fixed coveralls.io button (#17)
• Fixed links in README (#27)