minor clean up
test changes, move all the array slice stuff (which is not implemented on sparrays yet) to one test
somehow never added length.m
subs supports lists, vectors, etc
white space changes
install notes: mention dill
cell -> sym
diff fix to call ctor
subs cleanup

use cell -> sym
allow mixing array and cell
autogenerated fcns work with componentwise ops on matrices
symfum (sort of) work again