Update examples to use new username

May as well have working examples
Doc: less ambiguous; we're talking about a Github object, not the website
Doc RequestBuilder: Rewrite docstring; it makes much more sense now!
Style wibble: Use else branch to show alternatives

Having multiple return-points is confusing. Let's at least indent the
alternatives to the same level
RequestBuild.__repr__: Display self.url instead of triggering "I don't know..."
Style: Reindent 2 -> 4 spaces