sync: support syncing specified arguments

sync: support syncing specified arguments

* m4/jm-macros.m4 (coreutils_MACROS): Check for syncfs().
* man/sync.x: Add references to syncfs, fsync and fdatasync.
* doc/coreutils.texi (sync invocation): Document the new feature.
* src/sync.c: Include "quote.h".
(AUTHORS): Include myself.
(MODE_FILE, MODE_DATA, MODE_FILE_SYSTEM, MODE_SYNC): New enum values.
(long_options): Define.
(sync_arg): New function.
(usage): Describe that arguments are now accepted.
(main): Add arguments parsing and add support for fsync(2),
fdatasync(2) and syncfs(2).
* tests/misc/sync.sh: New (and only) test for sync.
* tests/local.mk: Reference the new test.
* AUTHORS: Add myself to sync's authors.
* NEWS: Mention the new feature.