Release version 0.5.34

Release version 0.5.33

Make message signature verifications optional in VTN

This makes the verification of TLS signatures optional in the VTN, which
is useful if the VEN is using client-side TLS but no message signatures.

Implement event delivery callbacks

Version 0.5.30

Released version 0.5.29

This fixes various small bugs relating to stability and code examples.

Release version 0.5.28

Version 0.5.27

Release version 0.5.26

Release version 0.5.25

This version contains many fixes that were suggested by community
members. Thank you so much for taking the time to find these and 
for reporting them.

Fixed:
- Implemented Registration Cancellations
- The VEN will now stop if the VTN did not accept the registration
- The XML messages will now be logged more consistently if debugging is 
  enabled
- Fixed a deprecation warning from tzlocal (from apscheduler)
- The VEN will now not re-send its report registrations after it was
  re-registered itself
- VEN: Added duration to metadata reports
- VEN: Removed eiReportID from metadata reports
- VEN: Added dtStart to outgoing reports
- VTN: Update the created_date_time anytime the Event's status changes