hakmem 0.1.0

First release, of a learning project far from production; the README's
Status section says what to expect. One trait (Bits) over
u8…u128 and Wide<N>: runs, rank/select/positions, scans (prefix
XOR/OR, Gray, find_escaped, Kogge–Stone fills), compact/expand,
Hacker's Delight ch. 2 basics and Gosper's hack, SWAR byte lanes, delta
swaps and 8×8 board permutations, dilated integers and Morton codes,
slice and 2D-grid operations, Myers edit distance / search. Every
combinator ships with laws; laws are property-tested on all carriers
with and without BMI2/PCLMULQDQ and exhaustively for widths up to 16
bits. hakmem::cookbook explains how the shipped kernels were composed.
Every primitive has a constant-time portable definition; pext and pdep
follow Hacker's Delight 7-4 and 7-5. hakmem::rank9::Rank9 is an O(1)
rank/select directory over a borrowed &[u64], rank9 plus a
select9-shaped inventory, with storage the caller supplies, no allocator,
pinned to slice by laws.

API decisions before the first release: Word is open, with portable
defaults for the derivable primitives, so a carrier outside the crate
is one impl block and the laws are its acceptance test. rank_below
is rank everywhere. Run lengths and fill strides are total. Added
slice::positions, myers::distance (carrier chosen by pattern
length), permute::board8::{Dir, slide} for sliding attacks in all
eight directions, and, behind the alloc feature, rank9::Rank9Buf.