* github-seldaek/stability:
Add stability docs
Add test for Pool handling and refactor a couple things
Add support for stabilities in lock file
Infer stability flags for requirements that have an explicit version required of a lower stability
Add InstalledArrayRepository to make sure the root package is not purged by the Pool because of a lower stability
Basic handling of stability flags
Add list of stabilities to base package
Add minimum-stability flag on root package to filter packages by stability
Add CompositeRepo::getRepositories
Add package stability