Describe that the only portable way to deal with addresses is by using
getaddrinfo(). Describe that some ports may support tuple addresses using
"socket" module (vs "usocket" of native MicroPython).
This clarifies return values and the handling of invalid (e.g. newline)
characters.
Encoding conforms to RFC 3548, but decoding does not, as it ignores invalid
characters in base64 input. Instead, it conforms to MIME handling of base64
(RFC 2045).
Note that CPython doesn't document handling of invalid characters in
a2b_base64() docs:
https://docs.python.org/3/library/binascii.html#binascii.a2b_base64 , so
we specify it more explicitly than it, based on CPython's actual behavior
(with which MicroPython now compliant).
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".
This adds description of implied AbstractNIC base class, which should be
"subclasses" and implemented by a particular network device class.
This is just an initial step in that direction, the API and description
will be elabotated further.
The list starts with the simplest functionality - GPIO, proceeds to
communication interfaces (UART, SPI, I2C), the to time(r) related
things, then everything else.
For a couple of ports, there was information which directory is set
as current after boot. This information doesn't belong to "uos" module,
and is moved to boards' references (which actually already contained
information on which directory is chosen for boot, even if without
explicit mentioning that it becomes current directory, which is now
done).
This method isn't implemented in any port. It seemed to have originated
in cc3200 port, but actually never was implemented there either. In
general case, it's impossible to implement this method (for example, for
a perfect GPO, which has only output latch without any feedback look
into a CPU).
Both aren't part of generic Hardware API: It's impossible to implement
.id() method in a generic case (e.g., when Pin is instantiated by the
underlying OS/RTOS). .board attribute is an obvious space hog which
instead can be implemented on Python level if needed.
