v0.4.3 - Unprocessed notification fix

This is mainly a bug fix release to address problems introduced in v0.4.2, but also includes some minor enhancements:

• Fixed a bug introduced in v0.4.2 where listeners weren't notified of unprocessed notifications in most cases (#155)
• Improved readability of the output of the ExpiredToken#toString method (#153—thanks, @runr!)
• We now depend on Netty 4.0.26 (#154—thanks, @matzew!)