This commit adds the errno attribute to exceptions, so code can retrieve
errno codes from an OSError using exc.errno.

The implementation here simply lets `errno` (and the existing `value`)
attributes work on any exception instance (they both alias args[0]).  This
is for efficiency and to keep code size down.  The pros and cons of this
are:

Pros:
- more compatible with CPython, less difference to document and learn
- OSError().errno will correctly return None, whereas the current way of
  doing it via OSError().args[0] will raise an IndexError
- it reduces code size on most bare-metal ports (because they already have
  the errno qstr)
- for Python code that uses exc.errno the generated bytecode is 2 bytes
  smaller and more efficient to execute (compared with exc.args[0]); so
  bytecode loaded to RAM saves 2 bytes RAM for each use of this attribute,
  and bytecode that is frozen saves 2 bytes flash/ROM for each use
- it's easier/shorter to type, and saves 2 bytes of space in .py files that
  use it (for each use)

Cons:
- increases code size by 4-8 bytes on minimal ports that don't already have
  the `errno` qstr
- all exceptions now have .errno and .value attributes (a cpydiff test is
  added to address this)

See also #2407.

Signed-off-by: Damien George <damien@micropython.org>

Signed-off-by: Damien George <damien@micropython.org>

Make and CMake builds are slightly different and these changes help make it
clear what to do in each case.

Signed-off-by: Damien George <damien@micropython.org>

It's a bit of a pitfall with user C modules that including them in the
build does not automatically enable them.  This commit changes the docs and
examples for user C modules to encourage writers of user C modules to
enable them unconditionally.  This makes things simpler and covers most use
cases.

See discussion in issue #6960, and also #7086.

Signed-off-by: Damien George <damien@micropython.org>

Documents the micropython.cmake file required to make user C modules
compatible with the CMake build system.

Signed-off-by: Phil Howard <phil@pimoroni.com>

Add most formatting-only commits to this file so that when used with
git blame, these commits are excluded and the output shows only the
interesting bits.

Signed-off-by: Damien George <damien@micropython.org>

The default pins can be optionally configured by a board.

Fixes issue #6974.

Signed-off-by: Damien George <damien@micropython.org>

This commit implements basic NVS support for the esp32.  It follows the
pattern of the esp32.Partition class and exposes an NVS object per NVS
namespace.  The initial support provided is only for signed 32-bit integers
and binary blobs.  It's easy (albeit a bit tedious) to add support for
more types.

See discussions in: #4436, #4707, #6780

Also fix related problems with socket on esp32, improve docs for
wrap_socket, and add more tests.