docs: filesystems: Remove uneeded .rst extension on toctables

There's no need to use a .rst on Sphinx toc tables. As most of
the Documentation don't use, remove the remaing occurrences.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

docs: promote the ext4 data structures book to top level

Move the ext4 data structures book to Documentation/filesystems/ext4/
since the administrative information moved elsewhere.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

docs: move ext4 administrative docs to admin-guide/

Move the ext4 mount option and other administrative stuff to the Linux
administrator's guide.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

docs: create filesystem internal section

Create a new top-level section for documentation of filesystem usage,
on-disk format information, and anything else.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

ext4: import on-disk layout book from wiki page

Create the basic structure of the "new" data structures & algorithms
book to be ported over from the on-disk format wiki, and then start by
pulling in the introductory information.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

ext4: convert ext4.rst to restructuredtext format

Convert the existing ext4 documentation into rst format and link it in
with the rest of the kernel documentation.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>