Yes, the PYI holds a full list of the commands and constants. There is currently no online help like TGC has.
If you use PyCharm, it performs syntax coloration on the PYI to make things a little more readable. It also has code completion and context-sensitive help (using the PYI file).
Python does include a help command that can be used against anything to get its documentation. It works in the Python console of PyCharm, but I see now that importing the pyd in IDLE throws and error about not determining the read path, which I'll need to change. With this help command, one can import appgamekit then call help(appgamekit) to get all commands or help(appgamekit.create_window) to get help on a specific command.
The TGC help site can be used to get an understanding of how AppGameKit works. The Python commands are similar, but have been changed to the Python naming convention. You can then use the function help to see whether the parameter order has changed (mainly a concern for functions that allow one to assign their own ID to things).