V0.2.0 consistency checks

PR corresponding to #221 
There are a number of constructs that have this problem: "GetResult is the deferred result of a Get request, call Extract to interpret it as an X." Unfortunately `godoc` doesn't provide us with a good way to do this kind of cross-referencing easily. Can you use relative hyperlinks in godoc... ?

Another idea would be to document our conventions on gophercloud.io and hyperlink to sections there from the docs. We're still just replacing one set of boilerplate with another, though.

Long story short, I'm not sure what the best solution is, here.