Changelog

• 4613d06 Merge pull request #2 from sensu/check-impl
• 2677b88 update README with updated usage info and an explanation about rate metric calculation
• 3f268e4 update rate metric generation logic to deal with case where timestamp has not changed to avoid divide by zero situation
• e9555bc Don't print usage screen when there's an error
• 61b2b61 Rename CounterMetricCache to CounterMetricState
• 8953798 Code review comments
• d49e6d4 Code review comments
• ae55f29 Code review comments
• 3759ba9 Remove cache file from git
• f3aeb9b Remove debugging log statement
• 0ce3a71 Initial implementation
• 1af22a9 Initial commit