Bump cernan to 0.3.4

This release has three major changes over 0.3.3:

   * a durable mpsc is now used in place of std's mpsc
   * QOS is now guaranteed timestamp accurate
   * Kinesis Firehose sink is introduced

In the situation of a very slow sink and a fast source cernan 0.3.3
and lower would allocate increasing amounts of memory. Obviously
that is not desirable but cernan cannot drop telemetry on the floor.
The solution is a durable mpsc which writes in-flight data to
disk in a concurrency safe fashion. Extensive testing has been done
to ensure safety of the durable mpsc.

In cernan 0.3.3 and below QOS was inaccurate as points would be put
into a timeless aggregation. A snapshot thread was added to simulate
time but this was less than perfect. Now we store points with their
timestamps in-aggregate and are able to do QOS elision with
guaranteed precision.

Finally, we introduce a Kinesis Firehose sink that will allow cernan
to emit into Amazon's Firehose, forking from there to various AWS
services, S3 and Elasticsearch of the most interest. At present this
sink only ships LogLines but in the future when #39 lands we can
choose to do more exciting things.

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

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "cernan"
-version = "0.3.3"
+version = "0.3.4"
 authors = ["Brian L. Troutwine <blt@postmates.com>"]
 build = "build.rs"