src/engine/SCons moved to SCons, affects wired in paths
in documentation, and doc building scripts

Signed-off-by: Mats Wichmann <mats@linux.com>

Eliminate some "note" wording in manpage. This is a "tone" thing,
trying to avoid so many "asides", like "Note that blah blah", by
trying to reword into a more regular flow, and occasionally dropping
the aside if it doesn't seem quite suited to the manpage.

More harmonization of docbook entity usage, cleanup
of comments around generated sections, and other fiddling.

<literallayout> around a code fragment was changed to <programlisting>
<literallayout> around output was changed to <screen>
If a <screen> section contained use input, that was marked
with the <userinput> entity.  These changes ought to also
facilitate better conversion to other document markup formats,
something which has been discussed.

In the Description section, the remaining command-line discussion
at the end was merged into the earlier wording about command-line
processing, to improve the flow a bit.

Some options entries were adjusted for appearance - indents, etc.

Mention of Python 2.7 as a requirement is dropped.

Signed-off-by: Mats Wichmann <mats@linux.com>

Also cleaned up a couple of doc typos.

- added missing icons for XXE4
- adapted schema location, such that the validation works properly in SernaFree and XXE

- accordingly updated the generated files, containing example output

  folder and all additional documentation sources get packaged properly
- added basic support for wildcards and recursive globbing in MANIFEST files
- added missing JPG/SVG files

- corrected the doc folder SConscripts and added XSL and titlepage files where required