Initial AsciiDoc -> DocBook -> XHTML mvn toolchain

In this commit, `mvn -N -Psaxondoc package xml:transform` builds the
AsciiDoc source docs/index.txt into a DocBook file,
`target/generated-docs/index.xml`, which is then transformed with
Saxon using the xslthl extension for syntax highlighting to produce
the XHTML document `target/generated-resources/xml/xslt/index.xml`.

common.xsl is taken from AsciiDoc; htcust.xml is a half-page so-called
"customization layer" stylesheet that glues together common.xsl with
xslthl highlighting.

This is the earliest proof-of-concept stage.  Much work remains in
both tweaking the XHTML style to fit with the new Titan website and in
porting the existing wikidocs to AsciiDoc before this could be
considered ready for distribution.
Switch to HTML 4.01 Transitional and DocBook 5

The current latest version of the AsciiDoctor maven plugin defaults to
DocBook version 4.5.  According to this issue, AsciiDoctor's default
DocBook version is changing to 5.0 in AsciiDoctor 1.5.0 (which has not
yet been released):

  https://github.com/asciidoctor/asciidoctor/issues/554

This commit forces docbook5 generation on the current AsciiDoctor
plugin by setting the backend to "docbook5".  This commit also
modifies htcust.xsl to generate HTML with the 4.01 Transitional
DOCTYPE and set the output encoding to utf-8.  The generated HTML
currently validates on http://validator.w3.org/check.  I also turned
on indentation in the HTML generator.
Add Titan website header spew to htcust.xsl

The wall of CSS in particular should ideally be in a separate file
that gets included, but this commit at least shows that it's
technically possible to get our new sticky Titan website header on the
DocBook output.
Refactoring asciidoc profile in top-level pom

AsciiDoc->DocBook->HTML now builds when "-Dasciidoc" is given on the
maven command line.
Refactor DocBook customizations for reuse

Extracted Titan CSS, HTML header tags, and main content wrapper tags
into XSL templates for shared reuse in single-file and chunked-file
HTML output.

Moved XSL sheets into subdirectory of doc.

Removed unnecessary "images/" prefix in relative image references in
AsciiDoc source.  AsciiDoc's backend attribute "imagesdir" is the
preferred way to control the directory prefix for image references.

Added a XSL stylesheet for chunked Titan documentation.  It compiles
as XSLT and produces output, but the CSS style is broken; there's ~500
pixels of dead space between the static header and the start of
content on every page.  More work needed before the chunked output is
remotely usable.
Ignore Emacs file backups (*~)
Remove "images/" prefix in AsciiDoc sources
Reenable syntax highlighting in singlefile docs
Fixes for chunked HTML DocBook output

* Remove dead space between sticky header and main content in chunked
  html output (singlepage html output did not have the issue to begin
  with); need to manually copy css to see effect of the fix since
  copying static assets isn't automated yet

* Modify titan.body template in titancommon.xsl to use <xsl:copy-of />
  so that it can be more shared between the chunked and single-page
  XSL stylesheets

I've completely cut out the next/prev navs at the top and bottom of
the chunked output.  Next step is probably to restore these links by
embedding them in the the static and sticky page header at the top and
just above the copyright footer at the bottom.  This will probably
involve splitting the titan.body template in titancommon.xsl into a
number of smaller component templates.
Switch to the "book" DocBook output type
Add nav footer back into chunked html docs

The nav footer returns -- it's functional again, but the style is
still vanilla and pretty ugly.  The nav header is still out.  Making
it play nice with the sticky/static Titan:db header is going to take
some additional style work that I don't want to get bogged down in
yet.
Adding text under the Storage Backends doc section
Copy static css and images for HTML docs

Added top-level pom stanzas to copy static assets from the doc
directory to the targe/docs/(htmlsingle|htmlchunk)/ directories.  No
more manual copying.
Show section titles in bottom nav links
Add one-sentence summary to management section

This makes viewing the docbook-generated chunk associated with the
management section a bit less disorienting.  Modeled on the approach
taken by the PostgreSQL manual.
Style doc html navigation footer
Restructure headings in intro and using docs

This organizes the the chunked HTML output into reasonably-sized pages
and also eliminates all of the warnings about section levels appearing
out of order that lingered in the AsciiDoc I recently ported from wiki
markup.
Bringing back the navheader

I think I'm going to disable it again in the next commit because it's
kind of annoyingly redundant with the header at the top of each page,
but now the markup and style plumbling is in place to turn it back on
with a one-liner if we want it.
Disabling nav header in chunked HTML doc output
Minor documentation CSS color tweak