Generate multiple report formats in one go

[hauleth]

Currently it is hard to generate for example HTML report and Cobertura XML report at the same time. It would be really handy to be able to define multiple output formats in a way like:

$ mix coveralls --format=xml --format=html

That would generate both - HTML and XML formatted output in one pass.

[juhalehtonen]

Thanks for creating this issue @hauleth! Have you happened to discover any workarounds for this, aside from running the whole test suite via mix coveralls twice, once for each format?

[smaximov]

I believe this was recently covered by #303