Auto merge of #74 - kvikas:master, r=Ogeon
Auto merge of #74 - kvikas:master, r=Ogeon

Implement Handler for Arc

Implement Handler for Arc and Box

1. Handler trait impl for Arc<T> calles handle_request() on T.
2. Handler trai can not be implemented generecally for Box without
conflicting with trait impl for Fn(). So implemented for Box<Handler>.
Clients need to cast their Box<T> as Box<Handler> to use this.

Fixes #70

kvikas/rustful,kvikas/rustful