git-filesync 0.22.0

Linked directories: add DIR links the directory, pull adds and deletes files

Changes:

• add URL|SOURCE DIR links the directory as one [dir] entry (base: upstream
  commit and tree). Its files are those of the upstream directory that its
  --include/--exclude patterns select. pull also fetches files new upstream,
  deletes those deleted there and merges adaptations (adaptable); a file
  renamed within the directory takes its adaptations along. No command
  touches files of your own in the directory.
• status shows a linked directory in one line, with the number of files
  concerned: "adapted: lib/ (1 of 40 files)".
• A file of a linked directory that is missing is never allowed, as for a
  linked file - unless upstream deleted it too: then pull stages the
  deletion.
• pull --force keeps a file of this repository that pull would delete
  (adapted here, deleted upstream) or replace (new upstream, in an
  adaptable entry).
• set --include/--exclude (--no-include/--no-exclude) change the patterns of
  a linked directory, at once; set -p makes it a new link.
• status, diff, difftool and restore also take files in a linked directory;
  pull, set, rm and unlink take the whole entry; mv moves the directory with
  your own files. Entries must not overlap.

Compatibility:

• add URL DIR now creates a [dir] entry; the previous behavior (a [file]
  entry for each file) is add --per-file. Existing [file] entries stay
  valid; to switch, unlink them (the files stay), then add the directory.

Documentation:

• MANUAL: new section "Linked directories"; add, pull, set, rm, mv,
  restore, diff.
• Pinned example versions in README and MANUAL set to v0.22.0.