Add section shortcode, to render children

exampleSite/content/docs/shortcodes/section/_index.md

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+---
+bookCollapseSection: true
+---
+
+# Section
+
+Section renders pages in section as definition list, using title and description.
+
+## Example
+
+```tpl
+{{</* section */>}}
+```
+
+{{<section>}}

exampleSite/content/docs/shortcodes/section/page1.md

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+# Page 1

exampleSite/content/docs/shortcodes/section/page2.md

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+# Page 2