simple transforms

Removes the old transform classes and machinery to make simple transforms use history under the hood.
Changes the `add_transform` method to accept a string naming the simple transform and a window length (unless you pass returns).

simple transforms are now actual methods on the SIDData that do internal calls to history and apply the proper transforms.
This is needed as part of the update to siddata, I think this should be in the main commit because without this part, neither will be standalone changes