Feature: add_hyperparams() and not just set_hyperparams()

[guillaume-chevalier]

This is in the case we want to override just 1 param and not each one. I thought this was done by default in the set method until I faced a bug.

TODO: we might find a better name than add_hyperparams. Perhaps add a flag to the setter, like set_hyperparams(..., update=True) where update will call self.hyperparams.update(new_hyperparams) instead of overriding them.

[guillaume-chevalier]

note: the random search and AutoML loops should use add params rather than set params, because sometimes there might miss some spaces or distributions so when that happens, we'd need not to overwrite the existing default params (those who don't have spaces).

@alexbrillant

[alexbrillant]

Fixed here #195