This PR removes use of the customized zephyr_docs_theme, replacing it
with the new read_the_docs theme. It ignores the tags that were
previously used to switch the theme for "development" vs. "daily" or
"release" and always uses the RTD theme. (The "daily" vs. "release" is
still honored to change the breadcrumb and doc version to "latest" if
"daily" is specified (as we did for the current doc build process),
otherwise it uses the version extracted from the
VERSION file in the source code (as would be appropriate for the docs
for a tagged release.)
This also pulls in using template extensions for breadcrumb and the
notice about latest having more up-to-date content when the "release"
tag is set.
Signed-off-by: David B. Kinder <david.b.kinder@intel.com>
5c8398da05