DNF, a new Package Manager

Summary

People are asking why we didn't choose to adopt zif instead of fixing yum. The reasons are:

dnf looks for a middle ground between a sane API and some backwards compatibility.
we ultimately want unified resolver across the stack and dnf and hawkey is the first step towards that.
using libsolv allows us to get closer to what SUSE uses. So it makes the RPM world easier to deal with.
Libsolv is a well tested and proven code base, currently the most sophisticated and optimized dependency solving implementation.