Improve message for InvalidFormatError and make misformatted int flags return status 400 rather than status 500
Merge pull request #4 from mailgun/invalid-parameter

Improve message for InvalidFormatError and make misformatted int flags return status 400 rather than status 500
fix README example code.
Make RestHelper interface compatible with package testing
remove unused import of gopkg.in/check.v1
Merge pull request #5 from mailgun/jeremy/testutils

Make RestHelper interface compatible with package testing
Added vulcan middlewares support.