Added metrics and run on exit

I need to collect metrics so we can determine what rate limits we are hitting and optimize our code. Everything runs in a docker container, so we can't just save the metrics to disk.

We have added the following to address these issues:

• perform-on-exit will run exactly once when the original command completes. It will run regardless of failure or success.
• metrics-enabled will enable the collection of metrics regarding retries and save them to eb-metrics.csv wherever eb is running.

The two commands can be combined to collect metrics, and place them in non-volatile storage.

0.0.5

Added

• Fail on string matches
• Fail on regexp matches
• Fail unless string matches
• Fail unless regexp matches
• Print friendly retry message
• Print verbose retry message

0.0.4

No functionality changes.

Alter license files, prepare for open source release.