Bump to 0.5.0

This release is a long time coming and closes the venerable 0.4.x
series of development. Cernan has been put on a good foot for
being open-sourced, has received significant optimizations and
been given three new sinks and one new source. The changes are
as follows:

  * ccced68 :: Telemetry now avoids allocing a CKMS if not needed
  * 3d88add :: mpsc is split out into the open-source hopper
  * 3937bc4 :: native protocol is introduced, Arc sprinkled throughout
  * 22668f4 :: Experimental InfluxDB sink is introduced
  * 4746766 :: Numerous small allocations in text sources are removed
  * f48403a :: Experimental Prometheus sink is introduced
  * 4b609f3 :: Cernan's internal data-model becomes that of native protocol
  * b1d482f :: Aggregation optimizations, wrt cache access

There were a few things I skipped in the above either because they
were later supplanted or because it was hard to fit the summary in
a short line. But that's the gist!

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

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "cernan"
-version = "0.5.0-dev"
+version = "0.5.0"
 authors = ["Brian L. Troutwine <blt@postmates.com>"]
 build = "build.rs"