Move pages under tldr, lint run.sh, update docs

tldr/xml-escape

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+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# xml escape
+
+> Escape special XML characters, e.g. `<a1>` → `&lt;a1&gt;`.
+> More information: <http://xmlstar.sourceforge.net/doc/xmlstarlet.pdf>.
+
+- Escape special XML characters in a string:
+
+`xml escape "{{<a1>}}"`
+
+- Escape special XML characters from `stdin`:
+
+`echo "{{<a1>}}" | xml escape`
+
+- Display help:
+
+`xml escape --help`