MiddlewareChain usage and interface

[marbemac]

Here, the comment says that middleware chain implements the middleware interface:

https://github.com/mailgun/vulcan/blob/master/middleware/chain.go#L10-L14

However, I don't see a ProcessRequest or ProcessResponse method on MiddlewareChain.

By contrast, ObserverChain correctly implements the Observer interface.

In general, how does one add a MiddlewareChain to a LoadBalancer? I quick example would be very useful!

I'm just getting into it - thanks for this fantastic package.