Travis-CI and 'Tests' project

I've added an xcode project for Travis-CI to build and test.

I was going to just build one of the example projects, but the choice was arbitrary and now we can have stricter build settings in the test project. The test project has all warnings on and warnings as errors, I followed the test project settings in [nicklockwood/OSCache](https://github.com/nicklockwood/OSCache).

:warning: I have **not** written tests! Just one to get started.