added some util funcs for making alt features
changed one bird to allow specification of different features, specification of hypers, ability to turn off auto-loading of observations. synthetic.py contains simple utilities for taking functions on a grid and generating a y,d,cell,cell feature dict (using vlads utils.py to convert the python dict to a venture string).
added multinomial to model and appropriate birds moves func. though need to check scopes
added filter and stuff for multibirds (in onebird)
added get all bird positions method for unit object