Add a command line parse command for local debugging

[gfr10598]

This change is 

[coveralls]

Pull Request Test Coverage Report for Build 6788

• 349 of 474 (73.63%) changed or added relevant lines in 5 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.7%) to 64.422%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
parser/pcap.go	10	13	76.92%
active/throttle.go	8	15	53.33%
active/poller.go	10	20	50.0%
cmd/parse/parse.go	72	111	64.86%
tcp/tcp.go	249	315	79.05%
<!--	Total:	349	474	73.63%	-->

Files with Coverage Reduction	New Missed Lines	%
parser/pcap.go	1	75.68%
<!--	Total:	1		-->

Totals
Change from base Build 6733:	0.7%
Covered Lines:	4094
Relevant Lines:	6355

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💛 - Coveralls

[stephen-soltesz]

I like the idea of a command line parser. Closing this PR to clean up open PRs.

The idea for a command line parser tool references this PR as an example. https://github.com/m-lab/etl/issues/1082