Refactor Sweep class

[rm875]

Implement the following suggestion:

At a high level, I think the approach is good, but it's better to make things simpler instead of stuffing everything into one class/dict.

E.g. at the least I think instead of search_space this class should take the 4 kwargs of fixed=None, zipped=None, grid=None, and random=None. Or, preferable, have 4 classes that each takes different parameters. E.g. FixedSweep and then the users can specify a list of these sweep classes, each used for one or more different parameters to sweep. Because I don't think these different methods have to ever be combined, right!?

Then, it would be nice if we could specify the parameters in a call to a function to the class. E.g. you'd do something like this:

class GridSweep(BaseSweep):
    def __init__(self, num_combinations=None, ...):
        super().__init__(...)
        self.num_combinations = num_combinations
        self._search_space = {}

    def add(self, **kwargs)
        self._search_space.update(kwargs)

    def __call__(self):
        if not_computed_yet:
            compute_comb
        return combinations

So then, you can use it in a much nicer way instead of stuffing everything into one init call:

grid = GridSweep()
grid.add(a=[5, 7], b=[3, 9])
grid.add(c=[88, 12])
combinations = grid()

Originally posted by @matham in #1 (comment)