Add Codecov to test PRs and Branches

[mariobehling]

codecov.io is test coverage solution that is free for open source projects. Please add it and change the badge on the Readme.md to eventyay-tickets.

[irfan-iiitr]

I would like to work o this . I went through the docs of codecov.io and i think i can implement it. May I get some information about what commands are used to run the tests or the location of file that has this information.