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