Use Meson in CI

[Martinsos]

Now that we have Meson as build tool, we would like to use it as main build tool in the CI.

Here are some suggestions on how to do this:

#161 (comment)
#161 (comment)

[cdunn2001]

I'm simplifying the travisci setup for jsoncpp.

I have to say that homebrew makes OSX setup so easy, I'd recommend it. I don't think you need to bother with pyp for ninja. No real advantage on OSX.

Actually, the whole meson/ninja setup is pretty easy. cmake is harder.

I'd recommend copying our travis/appveyor stuff, but your linux/cmake build is already faster than ours. (I think ours is slower only because we use cpp-coveralls for code-coverage.) In theory, one big advantage of our current setup over yours is sudo: false. Without sudo, TravisCI can use a VM for your build, so it finds an available host quicker. At least, that used to be true. Today, it seems like everything is pretty quick.

So here is what I recommend for now: Add meson to your homebrew section of .travis.yml for OSX (where you already have ninja), and build your code twice on OSX in a single job: Once with cmake and once with meson. That's very quick (< 1min) and easy to maintain.

Good luck!