Convert CLI to cmdliner, begin CHANGES

A number of command-line processing changes including switching -l/--local to --remote, -p/--prefix to --prefix, changing the default prefix to / rather than the output directory, and making access log parsing optional
Don't include the built Version module
Fix version interface bug
Update README with new cmdliner dep, changed CLI options, fixes OCamlPro/opam2web#46
Ignore autogenerated version.ml
opam2web version/revision and dirty flag are now exposed in meta generator
Merge pull request #47 from dsheets/cmdliner

Convert CLI to cmdliner, begin CHANGES