v3.0.0-rc

This release includes these features and fixes:

• --downloadonly option
• a few resource leaks and other issues uncovered by coverity
• fix the --cacheonly / -C option
• a spec file to build RPMs for tdnf
• delay refresh of the repo metadata until command line is validated
• print improvements
• support the --exclude option for all altering commands
• download options (retries, timeout, minrate and throttle)
• read multiple keys from one file
• ssl options

and other fixes.