Add a persistent connection for librato

When sending metrics and annotations to librato, use a persistent HTTP
connection.  clj-http.conn-mgr/make-reusable-conn-manager options can be passed
as a final map argument to librato-metrics to control the number of threads
used (default 4).
Use update-annotation
give the vm a bit more time
Merge pull request #293 from pyr/master

Give the vm a bit more time, helps openjdk6 not failing
avoid extra blank lines in logs
Allow a specifying different layouts

There are a bunch of things people might be interested in doing
wrt to riemann logging configuration. I tried to capture the most
common use cases, leaving more advanced configuration to people
willing to just drop in their log4j.properties file.

This code does not modify the existing behavior and thus will
not introduce inconsistencies for already configured riemann
instances.

It does add the following:

* ability to disable console logging
* ability to log to multiple files
* a choice of 3 layouts: the existing one (:riemann), :json-event(-v1)

The layout used for console output is specified with :console-layout
and defaults to :riemann, like today. Specifying a different layout here
can help people using runit to supervise riemann, since runnit expects
console logging.

The :json-event and :json-event-v1 layouts are useful for people shipping
riemann logs to logstash or elasticsearch and seems like a wide enough
standard (and a light enough dependency) to make the cut of riemann core
dependencies.
Merge pull request #295 from pyr/feature-json-event

More flexible logging configuration, JSONEvent support
flag /etc/default/riemann as conffile

... to avoid each upgrade from over-writing it.
install "default" file to correct location

... as referred to in initscript and where it belongs to by convention,
on redhat based systems.
Merge pull request #296 from mfournier/2-packaging-fixes

2 packaging fixes
config/async-queue!: docstring points to executor-service.
Test for (where (... event ...))
Merge branch 'master' of github.com:aphyr/riemann
riemann.time.controlled: Use of with-redefs to be slightly more forgiving.
Merge pull request #297 from udoprog/udoprog/with-redefs

riemann.time.controlled: Use of with-redefs to be slightly more forgiving.
Merge pull request #285 from hugoduncan/feature/add-librato-persistent-connection

Add a persistent connection for librato
riemann.streams: Documentation and whitespace fixes
streams/scale: docstring example
Merge branch 'master' of github.com:aphyr/riemann
coalesce splits by host as well