Better startup messages and MQTT status messages

• MQTT status messages with statistics are now sent on every received file. The total
  number of files received and the number of triggers actually fired are included in
  the message payload. Resolves issue 146.
• Add a clear message after initialization indicating whether startup was successful.
  If it wasn't there's now a link to a troubleshooting wiki page for assistance. Resolves
  issue 167.
• Fix typos in the source code. Resolves issue 170.
• Fix typos in CHANGELOG.md. Resolves issue 168.