1.5.0

• Add new constant QUEUED_EVENTS_BATCH_SIZE to limit events sent once
  (related to #31)
• Add "Beats" transport (logstash-input-beats, related to #31)
• Add "timeout" argument to transport classes for more flexible
  setting
• Docs: better document the shared database between handlers (#30)
• Perform tests also against Python 3.7
• Docs: explain Formatter extra dict in more detail (#23)
• Docs: minor improvements