Update URLs to match current redirects

This introduces the following changes:

* URLs that redirect have been updated.
* Some unadorned URLs in the documentation
  are updated to use RST embedded link syntax.
* A redirect that occurred when building the documentation
  has been addressed in `documentation/conf.py`.

The following message was displayed when building the docs,
and this is fixed as a part of this change:

```
loading intersphinx inventory 'py' from https://docs.python.org/objects.inv ...
intersphinx inventory has moved: https://docs.python.org/objects.inv -> https://docs.python.org/3/objects.inv
```