This commit adjust the sphinx configuration to use the "Read The Docs"
theme, which has the advantage of allowing the navigation bar
(containing among other things a search bar, and the TOC) to stay
fixed while scrolling the contents of the page being read. This is
particularly useful to allow access to those features while reading
a long page, for instance.
TN: VB25-024
The name of this file is very long, and this limits on Windows hosts
the location where the documentation can be unpacked, due to the
maximum path limitation we have there. This commit reduces
the likeliness of this problem happening, by shortening the length
of that file.
Tested by rebuilding the documentation in PDF format.
TN: TC18-012
