Add option to deprecate entire tag libraries

[stiemannkj1]

VDLdoc currently allows developers to deprecate Tags and other library components via the vdldoc:deprecated element. Specifying this element as part of the taglib-extensions element should deprecate an entire library. It should cause a strikethrough to appear for all Tags, Functions, and EL Variables (consistent with how deprecation works for each individually). It should also strikethrough the library name wherever it appears, and add a deprecated description if included.

<taglib-extension>
    <vdldoc:deprecated>Please use <code>example</code> instead.</vdldoc:deprecated>
</taglib-extension>