[tz] Noda Time

[Paul Eggert]

Thanks, I've added the following:

<li><a href="http://nodatime.org/">Noda Time &ndash; Date and time API
for .NET</a> is similar to Joda Time, but for the .NET framework
instead of Java. It is freely available under the
<a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License</a>.</li>

with the following NEWS entry:

    tz-link.htm now mentions Noda Time.  (Thanks to Matt Johnson.)

Please let me know if there are any problems with this.

This is all in the latest experimental github version, as part of the following
patch:

https://github.com/eggert/tz/commit/eb03aa784c4bc00c7260f6117c4d752e60f3e707