Widen dependency version ranges. (#439)
Widen dependency version ranges. (#439)

* Permit itertools 0.10
* Permit ndarray 0.15
* Permit approx 0.4 and 0.5 (ndarray 0.15 depends on approx 0.5)
* Permit 0.8.x (previously limited to 0.8.0)
* Permit strum/strum_macros 0.20.x and 0.21
* Permit rand 0.8 (which was already a dev dependency)
rust-bio/rust-bio