Riemann protocol dissector

Homepage: http://riemann.io/

Sample capture:
http://files.avsej.net/riemann-sample.pcapng

Protocol definition:
https://github.com/aphyr/riemann-java-client/blob/master/src/main/proto/riemann/proto.proto

Implementor's guide:
http://riemann.io/howto.html#write-a-client

Bug: 10758
Change-Id: I28634453423127fe647eb92e48072a90a7f5d232
Reviewed-on: https://code.wireshark.org/review/5620
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>
Petri-Dish: Pascal Quantin <pascal.quantin@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
Reviewed-by: Anders Broman <a.broman58@gmail.com>