Fix errors in documentation generation.

I'm currently going through this repository, fixing errors in rosdoc2 documentation generation, starting with the tf2 package.

But I have a question (if anyone is listening!).

The conf.py in tf2 has a lot of extra, unneeded stuff, and I would like to remove the cruft. The stuff added for rosdoc2 I understand. But my question is this:

Is there any need to support other other modes of documentation generation, beyond rosdoc2? For example, there is code there that is only useful for one or more of the following documentation generations: htmlhelp, latex, man_pages, texinfo, or epub. None of these are needed for rosdoc2 generation.

The changes that are needed go beyond fixing the cruft in conf.py. For example, Vector3 is not documented due to a configuration error that I can fix. But the immediate question concerns the non-rosdoc2 cruft.

Start with the tf2 package's conf.py and the rosdoc2 documentation-generation setup. Check which listed output modes are supported or required, then verify the Vector3 documentation configuration; done means the relevant cruft is removed without breaking rosdoc2 generation and Vector3 appears correctly.