Newsticker: Use libxml instead of `xml-parse-region'. Fix some glitches. Clean up.

Newsticker: Use libxml instead of `xml-parse-region'.  Fix some glitches.  Clean up.

* lisp/net/newst-backend.el: Remove Time-stamp.  Rename variable
`newsticker--download-logos' to `newsticker-download-logos' and
make it customizable.
(newsticker--sentinel-work): Move xml-workarounds to function
`newsticker--do-xml-workarounds', call unless libxml-parser is
used.  Allow single quote in regexp for encoding.  Use
libxml-parser if available, else fall back to `xml-parse-region'.
Take care of possibly missing namespace prefixes (like "RDF"
instead of "rdf:RDF") when checking xml nodes and attributes (as
libxml correctly removes the prefixes).  Always use Atom 1.0 as
fallback feed type.  Rename `newsticker--download-logos' to
`newsticker-download-logos'
(newsticker--unxml, newsticker--unxml-node)
(newsticker--unxml-attribute): New.
(newsticker--parse-atom-1.0): Call `unxml' in case that embedded
HTML code has become part of the xml parse tree.
(newsticker--parse-rss-1.0, newsticker--parse-rss-2.0): Take care
of possibly missing namespace prefixes.
(newsticker--parse-generic-items): Code formatting. Typo.
(newsticker--images-dir): Add trailing slash.
(newsticker--image-get): Fix error message.

* lisp/net/newst-plainview.el: Remove Time-stamp.

* lisp/net/newst-reader.el: Remove Time-stamp.
(newsticker-download-logos): Rename variable
`newsticker--download-logos' to `newsticker-download-logos' and
make it customizable.
(newsticker--print-extra-elements): Add optional parameter
'htmlish for using html markup.  Amend list of ignored elements.
(newsticker--do-print-extra-element): Add parameter 'htmlish for
using html markup.

* lisp/net/newst-ticker.el: Remove Time-stamp.

* lisp/net/newst-treeview.el (newsticker--treeview-item-show): Use html
for formatting extra elements.

* lisp/net/newsticker.el:  Remove Time-stamp, Version.
(newsticker-version): Make obsolete.