[WIP] feature/persistent_queue

make sure to run `rake bootstrap` first. 

when you run logstash the following queue files will be created:
```
filter_to_output_queue
filter_to_output_queue.0
input_to_filter_queue
input_to_filter_queue.0
```
`filter_to_output_queue` is the metadata file and `filter_to_output_queue.0` is the paged data file.

for now most of the code lives in:
- https://github.com/colinsurprenant/jruby-mmap
- https://github.com/colinsurprenant/jruby-mmap-queues

```ruby
require 'json'

NL = "\n".freeze

require 'profile'

def slow_method
10000.times {|i| { "a" => rand(2) }.to_json + NL + { "a" => rand(2) }.to_json }
end
def fast_method
10000.times {|i| "#{{ "a" => rand(2) }.to_json}#{NL}#{{ "a" => rand(2) }.to_json}" }
end

fast_method
slow_method
```

````
ruby -rprofile teste.rb
  %   cumulative   self              self     total
 time   seconds   seconds    calls  ms/call  ms/call  name
...
 11.57     2.45      0.65    10001     0.06     0.57  Object#slow_method
  6.94     4.37      0.39    10001     0.04     0.51  Object#fast_method
....
```

so, maybe:

    "#{event.to_json}\n#{LogStash::Json.dump(event.metadata)}"