Migrate hydro power formulation library into API

[kdayday]

Currently, there are docstrings for formulations in the API, using non-references to the docstrings in the formulation library. To follow the Diataxis format, the formulation library should be with the api under a reference section.

• move APIs into reference section
• disperse formulation library into docstrings for each formulation Type
• ideally, this would likely manually break up the public API into sub-pages by topic (i.e. Formulations is its own page, rather than section)