[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

Depending on the code style guidelines and preference, I really like "return unless event..." instead of "return nil unless"