Add slather/Coveralls test coverage reports

[dasmer]

• Modify project file to generate code coverage metrics
• Add step to .travis.yml to install slather and send metrics to Coveralls
• Add .slather.yml to configure how we send metrics to Coveralls.
• Add Coveralls Badge to README.md

You will need to enable Coveralls for AlexDenisov/FrameAccessor. I ran slather locally and reported test coverage is 100% 🌟

[AlexDenisov]

Very nice feature, thank you @dasmer.
I didn't manage to find why coveralls needs commit access, maybe you can give me a point?
I'm pretty sure there is something obvious, but I can't blindly give an access to a third-party tool, 'cause I'm member of a few organizations with a bunch of private repos.

[dasmer]

@AlexDenisov I would refer to lemurheavy/coveralls-public#450. I believe Coveralls needs commit:status to generate coverage stats. I would defer to @nickmerwin for more info.

[dasmer]

It looks like test coverage isn't being reported correctly on Travis. Closing until I figure out why.

[AlexDenisov]

Got it, let me know if I can help you.

[dasmer]

Re-opening to test a fix

[dasmer]

@AlexDenisov: We're getting coverage reports now 💃

[dasmer]

Also, to give you some more insight on why coveralls.io asks for commit read access, the service gives you line-by-line data on how often a tested line is called on in your unit tests:

ie:

[AlexDenisov]

Great job, @dasmer!
Waiting for a travis build to see the new and shiny coveralls badge 👍

[MaximDzhezhelo]

Very good job)