Remove some deprecated functions and add missing warnings
Deprecate "groups" in Regex

* `Regex.groups` -> `Regex.names`
* :groups -> :named on `Regex.scan`
* :groups -> :named on `Regex.run`

Signed-off-by: José Valim <jose.valim@plataformatec.com.br>

Conflicts:
	lib/elixir/lib/regex.ex
:named -> :all_names
`Regex.named_captures/2,3` returns a map of binaries <-> values instead
of a keyword

Signed-off-by: José Valim <jose.valim@plataformatec.com.br>

Conflicts:
	lib/elixir/lib/regex.ex
Tidy up some final changes regarding regexes and deprecations
Update CHANGELOG