Spec for HAPROXYHTTP pattern.

We ran into parsing problems with this pattern and my first step was to
look at the tests. There were none so I took the apache log example and
adapted it for haproxy using the haproxy documentation format as the
example log string.

HELP! I am not sure why using date { timestamp =>
"dd/MMM/YYYY:HH:mm:ss.S" } doesn't set the event timestamp correctly so
the example uses mutate but at least passes.
Use date filter to set the timestamp from the haproxy accept_date
Remove date filter from haproxy parsing example.
LOGSTASH-1106 Adding additional file output path option documentation. This is to highlight functionality of the path option that was not previously documented, and to prevent additional pull requests for implementation of date-based log rotation.
unix input: remove socket in case of EADDRINUSE
Update HOSTNAME in grok-patterns

RFC952 states of a hostname: "The last character must not be a minus sign or period."
https://tools.ietf.org/html/rfc952

Some of the limitations in RFC952 were lifted by RFC1123, but not this one.
https://tools.ietf.org/html/rfc1123

The updated regex still allows single character hostnames, but does not allow the final character in any section to be a '-'.
added set metric output
bumped statsd-ruby to version 1.2.0 to support set metrics
Added configs for Datadog metrics.
Europe date metric compliance is dd/mm/yyyy
Parse and batch incoming metrics.
Fleshing out flushing logic.
Add support for SINCEDB_DIR to file input

This change allows you to change the destination of sincedb files without having to change the $HOME environment variable.  If set, SINCEDBB_DIR will override HOME as the destination of default sincedb files.
Added a test for the SINCEDB_DIR functionality

Setting SINCEDB_DIR in your environment allows you to override the target directory for sincedb files.  The added test verifies that this functionality works properly
Add support for device-level metrics.
Typo!
Merge pull request #513 from dfwarden/master-statsdoutput_sets

Add support for "set" statsd metrics to statsd output
Merge pull request #525 from tejaycar/master

Allow custom global sincedb target directory
Stub flush method
- thin out sized_queue in prep for future.