Working XRayUDPReporter and STORAGE_TYPE xray (#56)

This adds `XRayUDPReporter` which defaults to localhost:2000 or
AWS_XRAY_DAEMON_ADDRESS. This can be used in applications directly or
integrated with a zipkin-server where `STORAGE_TYPE=xray`

Note: this is experimental and makes assumptions about trace ID format:
See openzipkin/b3-propagation#6

pom.xml

@@ -18,7 +18,7 @@
     <parent>
         <artifactId>zipkin-aws-parent</artifactId>
         <groupId>io.zipkin.aws</groupId>
-        <version>0.7.2-SNAPSHOT</version>
+        <version>0.8.0-SNAPSHOT</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>