Use a ring channel to avoid blocking write of events (#2082)

* Use a ring channel to avoid blocking write of events

* Add eapache/channels dependency

vendor/github.com/eapache/channels/CHANGELOG.md

@@ -0,0 +1,17 @@
+# Changelog
+
+#### Version 1.1.0 (2015-11-22)
+
+Bug Fixes:
+ - The `Len()` and `Cap()` methods on several implementations were racy
+   ([#18](https://github.com/eapache/channels/issues/18)).
+
+Note: Fixing the above issue led to a fairly substantial performance hit
+(anywhere from 10-25% in benchmarks depending on use case) and involved fairly
+major refactoring, which is why this is being released as v1.1.0 instead
+of v1.0.1.
+
+#### Version 1.0.0 (2015-01-24)
+
+Version 1.0.0 is the first tagged release. All core functionality was available
+at this point.