store observes using pickle. added two methods: one stores and once can read either from a filename created at init for the object or from a given filename argument. we can cross-check correctness by comparing the counts we get here to the pics we get. these are poisson and so will be noisy, but we will get an an increasingly good picture as we up the total num birds
switched plotting to make_grid, moved make_grid to utils
tests are now functions. mse comp of bird locs
added function, not debugged yet, for doing hypers inference