Create headers of functions/classes

[vzg100]

We should create blank functions/classes with the expected input, documentation, and some unit tests for them. We can treat this as a skeleton to build on later. For example the stat functions we expect to use such as linear regression.

[julianstanley]

That sounds like a fantastic idea to me. It'll also be a nice way to slice up what needs to be implemented.

[eegk]

We have been doing this as far as I know. :3 I can add some more empty functions.

[eegk]

Please add more functions if required based on the package. We have some, others may be missing.