Split pmbootstrap and aports in two repositories

Created by: ollieparanoid

There are different release cycles, that make sense for aports and pmbootstrap.

• aports: always up-to-date
  • we could provide different branches like edge, 3.6, 3.5 which follow Alpine's branching model
  • but these branches need to be always up to date
• for pmbootstrap we could have a stable release every now and then
  • that way we could package it for pip and for some Linux distributions (AUR, Gentoo overlay, ...)
  • it would be a better experience for new users (install pmbootstrap through their distribution/pip, more stability)

A great benefit, that @MartijnBraam pointed out:

if you ship pmbootstrap seperately, then you can make pmbootstrap init manage the aports git repo and make it selectable between "edge", which is the latest master or a specific tag