Metrics now counts 300s as success

refs #88
Add 300s status code handling for metrics test
Merge pull request #93 from jpfuentes2/jf_metrics_dont_count_300s_as_errors

Metrics now counts 300s as success
Revert "Merge pull request #93 from jpfuentes2/jf_metrics_dont_count_300s_as_errors"

This reverts commit 68eb90a335c2aa7fbfc7fe1b87c92aa6cccf9455, reversing
changes made to 2163081a2839618f683c6fdaa1746f30bbbe2dad.
Implement parser for proposed Targets DSL.

Fixes #97
Add more Targets parsing tests
Maintain backward compatibility with standard target files by peeking ahead to the next value after reading a method + URL; if it's another HTTP method then short-circuit the header/body parsing and remember the peeked value for the next go-round
Use MatchString vs FindString
Merge pull request #98 from cwinters/targets-dsl

Maintain backward compatibility with existing target files
Use regexp.MustCompile
Update README
CHANGELOG
Remove whitespace
Implement HistogramReporter

Fixes #81
Update README
Extract and test Histogram logic
Update CHANGELOG