move: rpmUtils -> rpm.

rpmUtils is a weird name. Also non-PEPy. These things are important now
when dnf.rpm.detect_releasever() is about to be exposed in the API.
api: document client's responsibility to preset the substitutions. (RhBug:1104757)
remove: couple of dead-code methods in dnf.yum.config.
lint: clean up most lint messages in dnf.yum.config
bulid: add dnf/conf to cmake.
Detect distroverpkg from 'system-release(release)' (RhBug:1047049)

This at the same time drops the 'distroverpkg' configuration, there's no
indication anybody in Fedora ever used it and at the same time the new default
is supposed to be universal accross distros.
api: add dnf.rpm.detect_releasever()
Fix a missing s in the title
doc: replace Yum with DNF in command_ref.rst
fix traceback from broken string formatting in _retreivePublicKey(). (RhBug:1111997)
traceback in Base.do_transaction. to_utf8() is gone since 06fb280.
improve the 'got root?' message of why a transaction couldn't start. (RhBug:1111569)
doc: acknowledge the existence of plugins on the man page (RhBug:1112669)
syntax: replaced tab with spaces
fixed encoding of parsed config line (RhBug:1110800)
Fixed a minor typo in user_faq - 'intall' should be 'install'
cli: simplify exception handling more.
tests: cosmetic: conf.protected_packages is ignored, drop it in FakeConf.
api: add basic documentation for dnf.package.Package.
api: expose Transaction introspecting in the API. (RhBug:1067156)