This is the initial commit

This plugin will allow people to keep track of Logstash availability by sending the output (a string, a counter, or an epoch timestamp) out to some other monitoring entity.  The default interval is 60 seconds, but it can be as low as 1 second.
Any specific reason why `@host` is not part of the `Event#new`?
```ruby
 event = LogStash::Event.new("clock" => sequence, "host" => @host)
```