Make the try_* functions into FitStatistic.grid_search methods?

[cdeil]

I just read through the tutorial and I think maybe one aspect of the probfit API could be improved.

At the moment there are try_uml and try_binlh functions that evaluate the unbinned or binned likelihood function for a grid of values and return the best result as a dict.

Wouldn't it be nicer to have a FitStatistic.grid_search(parameters) method? (I didn't look if the different fit statistics, a.k.a. cost functions, have a base class, but that's what I mean with FitStatistic here, i.e. UnbinnnedLH and Chi2Regression and ...)