Add tests from QED-it report

[daira]

QED-it wrote some tests during their review:

• [ ] Num::into_bits_le_strict
• [ ] AllocatedBit::alloc_conditionally
• [ ] EdwardsPoint::assert_not_small_order

They also wrote Python and Go implementations of Jubjub, with additional test vectors for the Pedersen hashes, NoteCommit^Sapling, and GroupHash.