Refactor LMS bucket counter fixup into func.
Refactor LMS insertion into buckets into func.
Further refactoring of bucket insertions.

Adapt LMS insertion function so it can be used by S-type insertions as
well.
Fix incorrect name in comment from copy/paste.
Refactor/clean up insertion of L-type into buckets
Avoid overhead of clearing out work[] in rename().

work[] only contains positive values, so fill in with bitwise-negated
(negative) values. We can then tell based on the sign which elements of
work[] we inserted vice which ones just contain old data.
Speed up renaming at levels 1+.

When comparing LMS substrings at levels 1+, it's very easy to walk the
two hand-in-hand until you get a difference. This changeset implements
that (removing the old code that walked both substrings in full every
time).
Remove need for recursive calls to scan for S-type characters.

Instead, have rename bit-invert the S-type characters as it builds S1.
Extract common code in rename0/rename1.
Extract common code in level0/level1.
When possible, replace for loops with ranges.

Marginal speed improvements.