Use parallelism over multiplicity in ADVZ verify_share

[ggutoski]

verify_share is slow when multiplicity is large. There's some low-hanging fruit to be picked by parallelization. Use a par_iter (or whatever) at the following line:

jellyfish/vid/src/advz.rs

Line 565 in 89b9345

(0..self.multiplicity as usize)

Fix this issue and #644, then cut a new release for jf-vid.