Provide a way to customize badge color thresholds

[alechenninger]

It seems like the default color thresholds are awfully high. Even at 70%, coverage is still "red" implying this is bad.

It would be nice if an individual repo could set up their own target thresholds for what they find an acceptable level of unit test coverage, with pretty colors to match :).

High test coverage percentage numbers are not necessarily good: http://martinfowler.com/bliki/TestCoverage.html

And certainly what is considered good is up for debate: http://googletesting.blogspot.com/2014/07/measuring-coverage-at-google.html

Not a huge deal, but would be nice.

Thanks!

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Update: For what it's worth, while I originally opened this issue, I actually would prefer this not change from current behavior now :). I don't mind the psychological nudge to increase test coverage (even if not necessarily a good thing), and I like that a Coveralls badge of a certain color means the same thing on any repo. It would be a little surprising if you saw a "green" badge with 10% coverage, for example.