Some outstanding TODOs for v2

[Datseris]

I see them as I go through #187

• rewrite transfer operator based on the new API for the rectangular encoding. Done in Use new binning encodings for transfer operator #200
• OrdinalPattern docstirng and probably source code needs to be redone based on new encode API. Done in WIP: Address remaining todos for V2 #195.
• Same for GaussianCDFEncoding. Done in Adjust GaussianCDFEncoding and related stuff for new encoding API #199.
• Search source code for TODO comments. Address as many as possible, make the remaining GitHub issues and delete TODO from the source code. Done in WIP: Address remaining todos for V2 #195.
• separate the documentation of the entropy with hte entropy estimators into a different documentation block. especially since you say they compute differential entropy. Done in Clarify dicsrete vs. differential estimators #191.
• re-introduce other complexity measures. Done in Remaining todos for V2: Re-introduce complexity, plus some bug fixes #196.