Add code coverage via coveralls.io

[caniszczyk]

Code coverage is a good thing to show and results should show up at:
https://coveralls.io/r/twitter/hraven

Signed-off-by: Chris Aniszczyk zx@twitter.com

[caniszczyk]

Here's the typical output: https://coveralls.io/builds/922331

@vrushalic @jrottinghuis what do you folks think?

[coveralls]

Changes Unknown when pulling 620f15e on add-coveralls into * on master*.

[vrushalic]

Thanks Chris, this was something I had wanted to add for quite some time. Looks good to me.

Do you think we should mention the link (https://coveralls.io/r/twitter/hraven) somewhere like README or the description. I see it in that command in the README.md but I meant as a section that calls it out.

[caniszczyk]

I'll take that as a yes to merge :)

@vrushalic feel free to update the README if you wish, the more documentation the better. I only added the badge so you can see it next to the build results badge (generally that's where I look for these type of things, but that may just be me).