Discourage calling init() directly

[joshfriend]

The apple language docs always use Foo() style over Foo.init(). While both do the same thing, using .init() seems superfluous.

A check for this rule could find instances of the text .init and verify that it is not preceded by either self, or super.

[mbrandonw]

You would also want to allow things like optionalString.flatMap(NSURL.init(string:)).

[joshfriend]

Hmm, yes that would make this more tricky...

[norio-nomura]

implemented on #715 and #826