bump gradle, slf4j & netty
.travis.yml: properly run tests, print infos
UDPListener(Test): try fixing tests, always IPv4
Add tags support

Went with a simpler design than originally planned.

We might could if performance ever turns out insufficient,
but my thinking here is that if a pipeline needs higher perf,
it'd be better to create a dedicated listener and avoid
using tags altogether.

Closes #32.
StatisticsReporter: quiet on unknown version
fix all the tests
UDPListenerTest: fix Java 6 compatibility

Inet4Address.getLoopbackAddress() appeared with Java 7.
Merge pull request #64 from airbnb/pierre/actual_tags

Implement tags, early tests