Completely get rid of PyClass and PyInstance. (classobject.[ch] aren't empty yet because they also define PyMethod.) This breaks lots of stuff, notably cPickle. But it's a step in the right direction. I'll clean it up later. (Also a few unrelated changes, e.g. T_NONE to define a "struct member" that is always None, and simplification of __hash__ -- these are unfinished.)