Protocol 22-rc3 support

This release adds support for Protocol 22-rc3 and maintains backwards compatibility for Protocol 21 and Protocol 22-rc2.

See also: #46

Changes:

• The createdAt field from TransactionInfo is now an int again.
• The field pagingToken from EventInfo is not nullable any more and will be filled for any version.

If you upgrade from the latest stable release (1.5.6) please read the info in release 1.6.0beta1 first.