Release script for uploading Osx artifacts

[tachyons]

This project is using appveyor to upload windows binaries to github release, But the CI we use for osx build do not have built in support for uploading artifacts to Github releases, So we need to write a script to do that. More details here

Docs: https://cirrus-ci.org/guide/writing-tasks/
Sample script: https://github.com/cirruslabs/cirrus-ci-docs/blob/master/.ci/deploy.sh