minor #1279 [Docs] Some minor fixes: Typos, Notations, Formatting (bicpi)

This PR was merged into the master branch.

Discussion
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[Docs] Some minor fixes: Typos, Notations, Formatting

Fixes for:
* Notations: html > HTML; javascript > JavaScript; composer > Composer
* Typos
* Wrong function names: ``escaper`` > ``escape``; ``include`` > ``source`` (in new chapter about ``source``)
* Formatting issues, e.g. remove RST from code blocks, it's not evaluated
* Wording where code sample outputs something: returns > outputs
* ``true`` parameter for ``autoescape`` - not needed any more

Commits
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a21df95 [Docs] Some minor fixes: Typos, Notations