Documentation update for 4.1.0

[hardbyte]

Mostly just editing wording and trying to fix any funky rendering.

A few minor edits to content, and now a bit more restructuring.

Follows on from the great work in #1421

[zariiii9003]

There are a few new warnings:

/home/runner/work/python-can/python-can/doc/interfaces/udp_multicast.rst:18: WARNING: undefined label: 'other_virtual_interfaces'
/home/runner/work/python-can/python-can/can/interfaces/udp_multicast/bus.py:docstring of can.interfaces.udp_multicast.bus.UdpMulticastBus:18: WARNING: undefined label: 'other_virtual_interfaces'
/home/runner/work/python-can/python-can/can/interfaces/virtual.py:docstring of can.interfaces.virtual.VirtualBus:12: WARNING: undefined label: 'other_virtual_interfaces'
/home/runner/work/python-can/python-can/can/io/logger.py:docstring of can.io.logger.Logger:4: WARNING: py:class reference target not found: can.TRCWriter

[zariiii9003]

While you're at it, could you take a look at this? This should fix the readthedocs PR integration

[zariiii9003]

What do you think about moving these into separate files? So they just appear in the table of contents like Bus, Message etc...

[zariiii9003]

The docs look much more well rounded now, i like these changes a lot.

Something that i'm still not super happy about is this:

The BusABC class, as the name suggests, provides an abstraction of a CAN bus. The bus provides a wrapper around a physical or virtual CAN Bus. An interface specific instance of the BusABC is created by the Bus class, for example:

Talking about abstract base classes isn't a great intro for beginners imo. This is probably the first paragraph that a new user will look at.

[zariiii9003]

looks good 👍