"Mirror" commits to the `pipe-osx` repo, to use two `.travis.yml`s.

Travis' linter responds to the `os` key, but they don't do anything
with it yet.  Instead, let this repo use `language: c` (for a linux
build) and give `language: objective-c` to `pipe-osx`.  That repo
is just a submodule (back to this repo) and a custom `.travis.yml`
that runs `scripts/travis-osx`.
Initial AppVeyor build.

Essentially stolen from julia's Windows CI PR.  As there, we rely on
AppVeyor implicitly providing MSYS1 for a shell.
Bring in vagrant.

While we're at it, add CI status badges to the README along with
instructions for bootstrapping a virtual machine.

In the provision script, install some common packages that I've found
myself generally wanting on occasion.  Additionally, the kernel source
is needed for recompiling the vagrant kernel modules (if used.)