Make tz-link.htm more up-to-date.

* tz-link.htm: Mention xCal and jCal.
Mention Microsoft Windows 8.1 support for tz names.
CLDR data is available in both XML and JSON form.
Update two links (thanks to Oscar van Vlijmen).
Fix some formatting glitches, e.g., remove random newlines from
abbr elements' title attributes.
* NEWS: Document this.