1. Remove whole-document highlighting in some function links
2. fix the function alias `readwriteimagevideo`

2. change an external link to maintain consistency with the previous tutorial

literalinclude

literalinclude, dropped :lines:

See also #2101

In section "How do we get an Affine Transformation" subsection 2 there was a ' where there should have been a ` which caused the math to be rendered incorrectly.

content and renamed to a more sensible name. Also fixed a wrong link in the
actual display_image tutorial.

The main problem with extra modules is that they're located outside
of the OpenCV root, while Sphinx requires that all documents are
within the documentation root. To circumvent this, we create a
"fake root" and copy all documentation (as well as all files that
it depends on) there. It's a bit messy, but what can you do.

As a bonus, this eliminates the need to generate modules/refman.rst
inside the source tree.