DAR202, 302, and 402: Excess Return/Yield/Exception in protocol method

[PhilMacKay]

I'm opening a new issue specifically for Protocols. A similar issue was made for abstract method, see #54, and has been fixed (though it's still open).

A similar situation occurs when subclassing typing.Protocol. Typically, the method body of a protocol will be empty (or ...). Our team likes to document protocol methods since there are usually more references to protocols than to actual concrete classes in our code.
This leads to a lot of false positives on DAR202 (Excess Returns), DAR302 (Excess Yield), and DAR402 (Excess exception) on these methods.

I expect the fix would be similar to the one applied to abstract methods from #54.
I haven't yet looked at the code, but I may be able to create a PR myself if it's not too complex ;)

Edit: it also affects yield.

[terrencepreilly]

Sure, that seems reasonable. If you'd like to submit a PR, I'll take a look.