Add more `sphinxcontrib` extensions

[trustin]

See: https://github.com/sphinx-contrib

• emojicodes
• redirects
• googleanalytics
• examplecode
• imagesvg
• video

[trustin]

Tried all of the above extensions and found only the following works with Sphinx 2.1.2:

• emojicodes
• imagesvg

video worked partially but I decided not to add it because:

• autoplay option does not work.
• Cannot enable loop.