Release v4.5.3

• Fixes an issue with the res.message.user object containing two nested slack properties (#505) - thanks @shanedewael.
• Fixes an issue where messages from bots with no bot user may have had undefined value for res.messages.user (#507) - thanks @shanedewael.
• Increases consistency of EnterMessage and LeaveMessage events by swapping to the events which are garaunteed
  to be delivered (#296) - thanks @aoberoi.
• Fixes an issue where listeners were not matched because the text formatting did not properly account for messages
  without text defined but which do contain valid attachments, such as from IFTTT (#504) - thanks @aoberoi.
• Fixes an issue where messages were delivered to Slack out of order (#379) - thanks @aoberoi.
• Documentation improvements (#372, #468) - thanks @aoberoi.
• Adds node v10 to the testing matrix (#510) - thanks @aoberoi.