iptables.dump, null safety for common args
comments and check
missed a file
fix -m
use a process-queue to avoid xtables errors
Merge pull request #6 from bmeck/queuedSpawn

* Added queued spawn support to prevent XTables concurrency fail lock.
* Added an `iptables.dump` method to parse out `iptables-save`.
* Added an `iptablables.check` method to check the existence one or more rules from the selected chain.