Chkbit

chkbit adds a new `atom` mode to store all indices in a single file!

Also in this release:
- simplify command options
- add json config support
- log summary

- preserve modification dates of directories
- fix ignore
- improved help
- update dependencies

- also update modified files with `-a`
- add `-d` option to include dot files

- update flags (breaks -s -> -S, -f removed)
- new --add-only mode
- new --no-recurse flag
- track directories and report missing files/dirs (-m)

- track directories and report missing files/dirs

First Go release