Switch to "get" backend

[vgmoose]

The current master version consists of in-progress code that eventually turned into the get package manager, and was implemented in the Switch homebrew app store.

Fulfililing this issue should finally satisfy #10, and get's repo has system tests which also makes me feel better about the stability of this approach

[vgmoose]

Removed YAML parsing of old repo format, and starting using get in 83e3c93

Still requires further integration with the older format of "packages" and the progress bar to be hooked up to get.