Add common integer bit string ffs, fls, ctz, and clz.

Add common integer bit string ffs, fls, ctz, and clz.

(ffs x): find first set, 1-indexed with 0 for 0
(fls x): find last set, 1-indexed with 0 for 0 (same as integer-length)
(ctz x): count trailing zeros (same as ffs)
((clz n) x): count leading zeros in n-bit word x