Remove unnecessary -O2 and bump the version

Also remove `Example` as a top-level module (part of the package).
Instead leave `example` as a folder (so it won't be visible by default)
Add "Knapsack" and "LCS" benchmarks
Improve "quick-start" documentation

Also fix examples so they would work with latest Haskell version
Enable -O2 for benchmarks

Correct tag for this release
Update CHANGES for 0.4.1
Version 0.4.1

Mostly documentation fixes