Multi-line bitstring printing should print multiple bits per line

[jackfirth]

Instead of this:

(bitstring
 1
 0
 0
 1
 0
 0
 1
 1
 0
 0
 1
 1
 0
 0
 0
 0)

Bitstrings should print something like this:

(bitstring
 1 0 0 1 0 1 1 0
 0 0 1 1 0 0 0 0)

One byte's worth of bits might still be too little, but it's better than one bit per line. The amount of bits printed per line should definitely be a multiple of 8.