This splits the Sphinx tag option from SPHINXOPTS. This allows us to
specify the tag without having to remember to add -W and -t. It also
fixes not being able to specify the tag with make.bat on Windows.
While we are touching this, redundant SOURCEDIR uses are removed (main
is already the default) and the .github/workflows/publish-ide-docs.yml
script is fixed (ide directory no longer exists).
The doc/api is a legacy name, which is confusing in the current use, since all build targets are now APIs.
Today we have:
doc/common: Common configuration and settings between all targets.
doc/main: Main Pybricks documentation at docs.pybricks.com.
doc/ide: Documentation shipped with the Pybricks Code IDE.