Simplify unmarkedFit methods documentation

[kenkellner]

Have one exported method (like fitted) for all unmarkedFit objects. This method would then call an internal method specific to the fit type. Would make documentation a lot simpler.

• Remove unneeded class exports (Remove most unmarkedFit and unmarkedFrame classes from exports #12)
• fitted method (Refactor fitted method #14)
• residuals method (Refactor residuals method #16)
• getP method (Update getP methods #22)
• nonparboot method (Update nonparboot method #21)
• update method (Single method for update and make it more robust #18)
• simulate method (Refactor simulate method #19)
• parboot method (e99b0f4)
• predict method (Predict method updates #20)
• summary method (Consolidate summary methods for unmarkedFit #23)
• ranef methods (Consolidate ranef methods #25)
• getY method (bb93738)
• plot method (bb93738)