Log Message:
Update yelp-xsl to 3.18.1

3.18.1
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* Fixed broken selector entity in DocBook chunker (Robert Harris)
* Fixed various translations (Piotr Drag)

3.18.0
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* Updated translations:
  zh_TW (Chao-Hsiung Liao)
  pl    (Piotr Drag)

3.17.90
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* Updated localization templates, removing unused code
* Dropped db.chunk.chunks parameter in favor of selector entity
* Improvements to API docs

3.17.4
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* Updated translations:
  pt    (Pedro Albuquerque)

3.17.3
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* Support external info links topic, guide, and seealso
* Support for Mallard Sites in cache generator
* Drop P. prefix for parameter pages in docs

3.17.2
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* Embed Mallard+SVG directly in HTML5 instead of using <object>
* Added a top-level dita2html XSLT driver file
* Fixed a few XSLT validity errors
* Correctly handle image-only links in Mallard
* Set HTML5 DOCTYPE for non-XHTML output
* Make sure TTML spans are displayed inline, #746550
* Updated translations:
  oc    (Cedric Valmary)