Add continuous integration on macOS

[dtolnay]

No description provided.

[sayrer]

I'd like to help with this and #25. Do you have a CI service you favor, or is that part of the problem to be solved?

[dtolnay]

Hopefully Travis CI should be easy to get working. Something like https://github.com/dtolnay/link-cplusplus/blob/690c615e632d1f3ce5b9408b318b34642cd60e28/.travis.yml.

[sayrer]

OK, Travis CI is a fine place to start.

[sayrer]

Would you be open to adding Buck and Bazel builds to this? I'm not attached to a particular solution, but I'm not convinced the the description of cxxbridge-cmd is accurate yet.

[dtolnay]

I would prefer not to tie that together with macOS CI, but I've filed separate issues to track Bazel and Buck CI.

[dtolnay]

but I'm not convinced that the description of cxxbridge-cmd is accurate yet.

Now that we have build files for both Buck and Bazel and neither of them required source changes to the cxx crate or cxxbridge-cmd, hopefully you are convinced. ;)