Bump to 0.5.5

This release has a number of small fixes as well as improvements
to the filter subsystem. The changes are:

  * a0c5814 :: Config parse errors are now more clear
  * 77fd9d2 :: Graphite/Statsd may now be bound to DNS hostname
  * 9dbf4c6 :: Wavefront sink percentiles are now configurable
  * 9148b5e :: Filter payloads can now be cleared of all logs / metrics
  * dd0093c :: Internal ticks are 1/sec, filters receive ticks properly

Each individual commit contains further details. The wiki will be
updated shortly as appropriate. Heavy users of filters are recommended
to upgrade.

Signed-off-by: Brian L. Troutwine <blt@postmates.com>