format segment name, close #365 - #366

Thank you for the PR.

Your current implementation has not obvious limit of 10000 segments. I guess we should either assert it and throw an exception or add another parameter $data['segmentCountFormat'] to createLargeObject with default value %05d.

I also want to add an integration test for this case.

added the config option segmentIndexFormat with default value %05d and fixed the unit test.

also added isValidSegmentIndexFormat() to check proper format (has to produce different values for given format and different values, plus result has to have same string length)