Updated parsing and writing as text.
Updated parsing and writing as text.

- Parsing returns a (:document () …) entity instead of a list.
  <?xml> are transmitted as a :foreign entity, and
  <!DOCTYPE> are transmitted as a :definition entity.

- Comment text is trimmed of the <!-- and -->.

- The newline strings are removed (they were an useless artifact).

- The output of newline for some tags has been tuned for better
  reading of unparsed-html.

- Write-html-text has been improved (handles :document entity, ignore
  :foreign, :definition and :comment); handles :pre elements.

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