efl-mono: Allow doc XML tags to be nested

efl-mono: Allow doc XML tags to be nested

Summary:
This allows inserting nested tags like:
<example><code>bla bla bla</code></example>

The generate_tag_example() is currently unused but serves as an example.

Depends on D8585

Test Plan:
Not much, unless you want to manually call generate_tag_example()
(Which I have done, and it works, I promise).

Reviewers: lauromoura, vitor.sousa

Reviewed By: vitor.sousa

Subscribers: vitor.sousa, cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D8587