remove Quaternion multidispatch workaround

Rust has true multidispatch now, yay!
ignore all png and raw files

I keep multiple versions of the raw buffers. If I break something, at least the
render state would not be lost.
add command-line options to run in master or slave mode
replace fail! with panic!
allow specifying the port in master mode
add sender to send render results over network
implement the send task
print send task result
implement merging received images
implement pop_iter again

I just removed it from master, but it _was_ used in this branch, not
with a `RingBuf`, but with a `Vec`. So now this has a specialised
`pop_iter` for `Vec`. Again, I liked the generic one better, but this
suffices for now.