Fail to load $ref remote files in a remote file

[coryodaniel]

Remote files can be loaded, but when they reference other remote relative files apocryphal fails to load the file because it is looking at the local relative path.

Consider adding a diff method for starting parsing that continuing parsing, that way we can pass along the root path...

Apocryphal.doc(top_level_doc)
Apocryphal.parse(root_path, file_path)