Update to 1.20. Add some dependencies so that gtk-depscan runs.
Mark as not ready for python-3.x.

GTK-Doc 1.20    (Feb 16 2014)
============

Important notice - starting with the next release these long deprecated
features will be removed, please write to gtk-doc-list@gnome.org and tell us
your concerns:
o gtkdoc-scanobj (only used for gtkobject)
o return values need to be documented using "Returns:". We will remove the
  heuristic that turns a paragraph starting with "Returns " into return docs.
o gtkdoc-mktmpl - please move all the comments into the sources.
o generating html via sgml tools (jade/openjade), using xsltproc and
  docbook-xslt is pretty common and preferred since version 1.6

Changes

o 605537 : Returns: listed among parameters
o 624001 : Support attribute-based method to deprecate symbols
o 662424 : Class hierarchy about interfaces not generated by default
o 665926 : should not have to document object structures
o 666509 : Specifying --enable-gtk-doc should not be required to build source packages
o 669417 : Duplicate IDs generated for unions registered as boxed types
o 671519 : Self-test relies on nonportable (GNU enhanced) 'date' command
o 692367 : gtkdocize should take a srcdir argument
o 696570 : style updates
o 697940 : Race condition between setup-build.stamp and scan-build.stamp
o 701259 : /bin/bash: -chmod: command not found
o 701638 : Support automake parallel test harness (fix error with GTKDOC_CHECK)
o 706404 : Minor bug in gtkdoc-mkdb
o 706438 : Empty lines added at the beginning and at the end of a programlisting
o 707426 : master is broken in picking up flavour from configure.ac
o 707717 : Support " Deprecated: X.Y "
o 708268 : New *-insensitive.png files are not distributes
o 710478 : gtkdoc-mkdb: Don't complain about annotations with hyphen
o 711111 : gtkdoc-mkdb: sort entries in the glossary
o 711598 : gtkdoc-scan doesn't ignore decorators containing parentheses
o 719644 : docs: make yelp usage conditional in manual
o 719645 : configure: emit message when looking for yelp
o 720061 : make: create subdirectories of the content_files to the  builddir
o 721228 : configure: search for xml catalog in XDG_DATA_DIRS
o 722479 : cp -u is not portable
o 723118 : Mark |[ blocks as CDATA
o 723288 : Fix MarkDown support
o 723417 : New MarkDown parser
o 723696 : Add support for blockquote
o 723812 : Add support for reference links
o 723913 : List in markdown: < p > inside the last element of a < ul > list
o 723991 : Improve the display of the synopsis
o 724002 : gtkdoc-scan: Fix use of uninitialised value in trace logging

Contributors

Alban Browaeys
Alexander Kanavin
Carlos Garcia Campos
Christian Kirbach
Daniel Mustieles
David King
David Nečas
Dieter Verfaillie
Dimitris Spingos
Hib Eris
Matthias Clasen
Philip Chimento
Philip Withnall
Rafael Ferreira
Rico Tzschichholz
Ryan Lortie
Sebastian Rasmussen
Sébastien Wilmet
Stefan Sauer
Stef Walter
William Jon McCann
Zbigniew Jędrzejewski-Szmek

(wiz)