Add advisory object.
Add advisorylist object.
Add advisoryref object.
Add advisoryreflist object.
Add hy_package_get_advisories method.
api change: deprecate hy_package_get_update_*.
tests: add tests for advisory object.
tests: add tests for advisoryref object.
py: add _hawkey.AdvisoryRef type.
py: add _hawkey.Advisory type.
py: add _hawkey.Package.get_advisories method.
tests: py: add tests for hawkey.Advisory type.
tests: py: add tests for _hawkey.AdvisoryRef type.