Removes an unnecessary integer division in hashdyn.

This should be a little faster.
More documentation changes.
Reimplements the bucket addressing for hashling.

This new implementation allows the compiler to use
a conditional move instruction, resulting in an
addressing code without any conditional jump.
Uses a simpler statement to compute the split bit in hashlin.

That bit is already stored in the low_max entry, without any
need of computation.
Default run for valgrind is the check program.
Some documentation changes.