Optional "install" of updated version

[bhamail]

Issue #208 Update Check implements checking for new updates and notifying the user when they are detected.
In some environments, we may be able to install the update if desired via the selfupdater.

cc @bhamail / @DarthHater

[bhamail]

Would likely complicate the brew formula, as I think it would need to rebuild the binary. e.g. passing in compiler flags to rebuild the binary with compiler args to set the packageManager field.

see: https://github.com/Homebrew/homebrew-core/blob/master/Formula/circleci.rb