Refactoring "get_queued_job" method
Add the ability to [interally] retry "get_queued_job" based on the value returned from "get_queued_job_retries"

At this point there are no changes to the default functionality
Test stubs related to feature (WIP)
Use "ConcurrentRestriction" style configuration as opposed to relying on environment variables/defaults
Add tests to cover new functionality
Name "get_queued_job_attempts" to "reserve_queued_job_attempts"
Add documentation and tests for configuring "reserve_queued_job_attempts"
Lower slice-size used during "reset_restrictions" from 100K to 10K (it was causing segfaults when testing)
Merge pull request #5 from jzaleski/stash_restrictions_more_aggressively

Configuration support to allow for stashing of restrictions more aggressively