some performance things
remove loop over particles
add better StreamModel class, currently just skeleton
startign tests / api for stream model
laid out API
oops, here is where I laid out the API
changed from _x to _X
add galactic usys to top level
add unitless gc to heliocentric and reverse transforms
added observe() method for particles
whitespace mostly
renamed error model
add command line date spec
added parameter class
added tests for parameter class
change r_halo to R_halo, use new parameter scheme in LawMajewski2010
add fixed
totally lost
move stuff to observation
new observation module for triand stars