Allow parse method to be overridden

[nynexman4464]

I have an existing API returns entries in a different format than slickback expects.

I planned on overriding the parse method, so I could transform the object into the expected format, but I could not. Looks like slickback always replaces the parse method of the collection with it's version, even if I've specified my own.

Makes it really hard to work with an existing API.