Windows build

Enable building/installing on Windows machines. This requires `cmake`, a version of Visual Studio, and possibly a Windows SDK to be installed.

*(This is based on #49, so it may require some rebasing if there are changes to that PR.)*

- [x] `install.js` doesn't execute bash-only commands
- [x] `node-gyp configure` works
- [ ] Proper win32 `pthread`
- [ ] Resolve link errors
- [ ] Figure out what to do about `segfault-handler`
- [ ] Rebase on changes in #49