This system makes it a lot easier to include external libraries as static,
native modules in MicroPython. Simply pass USER_C_MODULES (like
FROZEN_MPY_DIR) as a make parameter.
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".
State that this doc describes generic, "core" MicroPython functionality,
any particular port may diverge in both directions, by both omitting
some functionality, and adding more, both cases described outside the
generic documentation.
We have enough terms or references throughout the docs which may be not
immediately clear or have some important nuances. Referencing terms in
gloassary is the best way to deal with that.
The old intro talked about "differences", but there were hardly any
sections describing differences, mostly MicroPython specific features.
On the other hand, we now have real "differences" chapter, though it's
mostly concerned with stdlib differences.
So, try to avoid confusion by changing wording and linking to the other
chapters and contrasting them with what is described in "MicroPython
language".