API corresponding to Gekko 3.1.12

Gekko is a free timeseries-oriented software package for timeseries data management, and for solving and analyzing large-scale timeseries-based models. An API is a description of classes, fields and methods. All the info shown here is also present in the form of comments in the source code, but the API can be easier to navigate for some purposes. Not all methods have explanations yet, but a lot of the most important have, for instance the methods in Program.cs, G.cs, and O.cs.