doc: improve documentation on --cacheonly. (RhBug:1066743)
refactor: MultiFileProgressMeter.end()'s status shouldn't default to FAILED.
refactor: how download progress are handled.

Introduces special Payload class hierarchy to handle the complexities in
between librepo and display callbacks.
remove: repo.get_package(), get_package_target().

Not used.
refactor: downloads of metadata use the Payload system too.
tests: fix the unit tests after Progress/Payload refactoring.
Turn DRPM into playing by the same Payload rules as RPM.
fup-drpm refactoring
added glob arch pattern support (RhBug:1048788)
fixed path to imported constant
refactored _nevra_to_filters function
remove: dnf.output.

Superseded by dnf.callback which is a more generic name.
doc: faq: simple installing rawhide packages.
rename: callback.Progress -> callback.DownloadProgress.

There might be other progressing things too besides network downloads.
api: document dnf.callback.DownloadProgress and friends.
refactor: Payload makes more sense to live in dnf.callback.
New version: 0.4.15
build: 0.4.15-1
refactor: Move InfoCommand._print_packages to BaseCli.output_packages.
refactor: Move repo-pkgs info to a standalone class instead of reusing the InfoCommand.