pgsql: doc: Add some images

doc: Add some images

Add infrastructure for having images in the documentation, in SVG
format.  Add two images to start with.  See the included README file
for instructions.

Author: Jürgen Purtz <juergen@purtz.de>
Author: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Discussion: https://www.postgresql.org/message-id/flat/aaa54502-05c0-4ea5-9af8-770411a6bf4b@purtz.de

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/ea55aec0a97d6cade0186df1913da2c8cb5c6f2c

Modified Files
--------------
.gitattributes                           |   1 +
doc/src/sgml/Makefile                    |  14 +-
doc/src/sgml/gin.sgml                    |  12 +-
doc/src/sgml/images/Makefile             |  18 ++
doc/src/sgml/images/README               |  61 ++++++
doc/src/sgml/images/gin.dot              |  93 +++++++++
doc/src/sgml/images/gin.svg              | 320 +++++++++++++++++++++++++++++++
doc/src/sgml/images/pagelayout.svg       |  40 ++++
doc/src/sgml/images/pagelayout.txt       |  11 ++
doc/src/sgml/storage.sgml                |  14 ++
doc/src/sgml/stylesheet-hh.xsl           |   6 +
doc/src/sgml/stylesheet-html-common.xsl  |   1 +
doc/src/sgml/stylesheet-html-nochunk.xsl |  11 ++
doc/src/sgml/stylesheet.xsl              |   6 +
14 files changed, 602 insertions(+), 6 deletions(-)