add updatePars method to Model class

part of building model object for more easily extensible modeling
suggested in Issue #8. Since several sim functions use parameters from
the model object now, but emcee needs a pars array (first arg to
lnProbVMapModel). This method glues those pieces together, updating
the model attributes when the pars array is updated. Also renamed
guess and guessScale array attributes, since interpretPriors now
writes abbreviated versions of those arrays to the model object when
there are fixed pars.
replace long arg arrays with model object in fit.py

interpretPriors, lnProbVMapModel, vmapFit, and fitObs all now
interface with the model object rather than lists of individual
parameters. The Model class should be pickleable so we can still
parallelize with emcee.
makeConvolutionKernel now takes model object

also removed deprecated args from vmapObs