Added Documentation to Adapter Transforms

[eodole]

Documentation added to:

• concatonate.py: not sure if the options are all correct... can inference_conditions" be specified as the into string?
• drop.py: this just seems like the opposite of keep, I'm not sure why we have both
• elementwise_transform.py : not sure what this does other than be a parent class

[paul-buerkner]

Thank you! please see my minor comments.

[paul-buerkner]

Thank you! We have both keep and drop because it may be more efficient to use either of the two depending on the application. Doc for ElementwiseTransform looks good.

[eodole]

I changed the documentation in

• standardization.py: I wasn't sure about the mean/std explaination, I could also remove saying that people should specify their own mean/std because im not really sure what the use case would be
• transform.py
• one_hot.py

[paul-buerkner]

I think this now looks good, thank you! Will merge now. About your standardize question: You are not sure what the use-case would be for the mean and SD inferred from data? Or the use case of a user-specified mean and SD?