Remove test/fixture/build from repo

This is a generated file and it is rebuild on every test. It doesn't
make sense to have it version controlled.
Add expectations for new gist syntax
Add expanded gist syntax

This add the ability for a gist in the YAML fron matter to designate a
specific file in a gist not just the entire thing.

    ---
    gist: expalmer/4bc6203dc2a3f7134e78 sukima/510438:load_config.rb
    ---

By appending a `:filename` to the list it will be parsed to the
followign url:

    https://gist.github.com/sukima/510438.json?file=load_config.rb

You reference the gist in the document the same way:

    gist:sukima/510438:load_config.rb
Provide better error reporting

When we have the power of Q there isn't much need to continue the
callback style.

Also the former method would cause issues if the return body from github
was bad JSON data (throwing a parse error). Since the logic is now in a
promise function it can be properly managed via Q.