simple mdlinter that checks the document's front matter

Arguments:
  [<target>]    can be file or folder, if folder files to process are detected
                recursively

Flags:
  -h, --help                    Show context-sensitive help.
  -f, --filter=REGEX            file detection filter when folder given, default
                                is \.md$
  -e, --fmkeys=KEY=VALUE;...    evaluate a distinct front matter key and its
                                value type, can be used multiple times (i.e.
                                -e index=int -e no=float -e title=string -e
                                tags=slice -e m=map)
  -s, --fmstrinct               strictly evaluate front matter, documents
                                are considered to be invalid if front matter
                                contains a key that wasn't provided with the
                                'fmkeys' arg
  -o, --invalid-only            print out validation result of invalid files
                                only
  -V, --version-flag            display version