Code review comment for lp:~albaguirre/mir/add-menu-api

As already discussed, I don't think it's a good idea to make make creation functions type-specific. The result is we'll have exponentially more API functions this way, and higher coupling to type-specific semantics. But I lost that argument and so will abstain... although there is a cosmetic issue that needs fixing:

(1) Headers containing documentation that will be read by users as such should be wrapped within 80 columns so they display in users' terminals correctly:
   include/client/mir_toolkit/mir_surface.h

We don't impose this standard on our own internal code, but the public stuff needs to be more consumable.