Previously individual ports documented these aspects to varying degrees,
but most of the information is common to all ports.
In particular, this adds a canonical explanation of `boot.py` and
`main.py`.
This work was funded through GitHub Sponsors.
Signed-off-by: Angus Gratton <angus@redyak.com.au>
Replaces "PYB: soft reboot" with "MPY: soft reboot", etc.
Having a consistent prefix across ports reduces the difference between
ports, which is a general goal. And this change won't break pyboard.py
because that tool only looks for "soft reboot".
With this commit there is now only one entry point into the whole
documentation, which describes the general MicroPython language, and then
from there there are links to information about specific platforms/ports.
This commit doesn't change content (almost, it does fix a few internal
links), it just reorganises things.
Angus Gratton