* dev: (34 commits)
  Add Travis badges to README
  Remove failing PHPv7.0 from Travis config
  Replace failing PHPv5.4 by v7.0 in Travis config
  Add missing composer requirements
  Add Travis configuration
  Add sample implementation and specs for SimpleAggregateRoot
  Add spec for AggregateUuid
  Add specs for SimpleDomainEvent and SimpleEventStream
  Add sample implementation and spec for ImmutableValue
  Add trait using windUp() for equals()
  Add SimpleAggregateRoot based on traits.
  Add several traits for implementing event-sourced aggregate roots
  Add AggregateUuid as implementation for EntityIdentifier
  Add simple implementations for events and streams in Basic
  Introduce abstract class AggregateRoot
  Introduce interface EventSourcedEntity
  Introduce interfaces EventStream and its descendent EntityHistory
  Move ImmutableValue to new sub-namespace Basic
  Restructure IDs and references makeing them all interfaces
  Refactor DomainEvent based on new interfaces
  ...