For modules I initially created or made substantial contributions to.

The original code called setsockopt(SO_RCVTIMEO/SO_SNDTIMEO) with NULL
timeout structure argument, which is an illegal usage of that function.
The old code also didn't validate the return value of setsockopt, missing
the bug completely.

1. Return correct error code for non-blocking vs timed out socket
(POSIX returns EAGAIN for both, we want ETIMEDOUT in case of timed
out socket). To achieve this, blocking/non-blocking flag is added
to the mp_obj_socket_t, to avoid issuing fcntl() syscall each time
EAGAIN occurs. (mp_obj_socket_t used to be 8 bytes, having some room
in a standard 16-byte alloc block.)

2. Handle socket.settimeout(0) properly - in Python, that means
non-blocking mode, but SO_RCVTIMEO/SO_SNDTIMEO of 0 is infinite
timeout.

3. Overall, make sure that socket.settimeout() call switches blocking
state as expected.

This mechanism will scale to to an arbitrary number of pollable objects, so
long as they implement the MP_STREAM_GET_FILENO ioctl.  Since ussl objects
pass through ioctl requests transparently to the underlying socket object,
it will allow ussl sockets to be polled.  And a user object with uio.IOBase
as a base could support polling.

This patch moves the implementation of stream closure from a dedicated
method to the ioctl of the stream protocol, for each type that implements
closing.  The benefits of this are:

1. Rounds out the stream ioctl function, which already includes flush,
   seek and poll (among other things).

2. Makes calling mp_stream_close() on an object slightly more efficient
   because it now no longer needs to lookup the close method and call it,
   rather it just delegates straight to the ioctl function (if it exists).

3. Reduces code size and allows future types that implement the stream
   protocol to be smaller because they don't need a dedicated close method.

Code size reduction is around 200 bytes smaller for x86 archs and around
30 bytes smaller for the bare-metal archs.

These defined couple of functions added during initial experimentation,
which aren't part of MicroPython API and no longer used or needed.

Unix naming is historical, before current conventions were established.
All other ports however have it as "modusocket.c", so rename for
consistency and to avoid confusion.

Header files that are considered internal to the py core and should not
normally be included directly are:
    py/nlr.h - internal nlr configuration and declarations
    py/bc0.h - contains bytecode macro definitions
    py/runtime0.h - contains basic runtime enums

Instead, the top-level header files to include are one of:
    py/obj.h - includes runtime0.h and defines everything to use the
        mp_obj_t type
    py/runtime.h - includes mpstate.h and hence nlr.h, obj.h, runtime0.h,
        and defines everything to use the general runtime support functions

Additional, specific headers (eg py/objlist.h) can be included if needed.

This is to keep the top-level directory clean, to make it clear what is
core and what is a port, and to allow the repository to grow with new ports
in a sustainable way.

There were several different spellings of MicroPython present in comments,
when there should be only one.

These checks are already made, and errors reported, by the uPy runtime.

Its addition was due to an early exploration on how to add CPython-like
stream interface. It's clear that it's not needed and just takes up
bytes in all ports.

One can instead lookup __name__ in the modules dict to get the value.

This includes file and socket objects, backed by Unix file descriptor.
This improves compatibility with stmhal's uselect (and convenience of
use), though not completely: return value from poll.poll() is still
raw file descriptor.

It's now used for more than just stream protocol (e.g. pin protocol), so
don't use false names.

By reserving enough space for peer address.

The first argument to the type.make_new method is naturally a uPy type,
and all uses of this argument cast it directly to a pointer to a type
structure.  So it makes sense to just have it a pointer to a type from
the very beginning (and a const pointer at that).  This patch makes
such a change, and removes all unnecessary casting to/from mp_obj_t.

With this patch the n_args parameter is changed type from mp_uint_t to
size_t.

This patch changes the type signature of .make_new and .call object method
slots to use size_t for n_args and n_kw (was mp_uint_t.  Makes code more
efficient when mp_uint_t is larger than a machine word.  Doesn't affect
ports when size_t and mp_uint_t have the same size.

This allows the mp_obj_t type to be configured to something other than a
pointer-sized primitive type.

This patch also includes additional changes to allow the code to compile
when sizeof(mp_uint_t) != sizeof(void*), such as using size_t instead of
mp_uint_t, and various casts.

Return tuple of (address_family, net_addr, [port, [extra_data]]). net_addr
is still raw network address as bytes object, but suitable for passing to
inet_ntop() function. At the very least, sockaddr() will separate address
family value from binary socket address (and currently, only AF_INET family
is decoded).

inet_pton supports both ipv4 and ipv6 addresses. Interface is also extensible
for other address families, but underlying libc inet_pton() function isn't
really extensible (e.g., it doesn't return length of binary address, i.e. it's
really hardcoded to AF_INET and AF_INET6). But anyway, on Python side, we could
extend it to support other addresses.

Required to implement UDP servers.

sendto() turns out to be mandatory function to work with UDP. It may seem
that connect(addr) + send() would achieve the same effect, but what connect()
appears to do is to set source address filter on a socket to its argument.
Then everything falls apart: socket sends to a broad-/multi-cast address,
but reply is sent from real peer address, which doesn't match filter set
by connect(), so local socket never sees a reply.

Treating it as signed lead to buffer overflow for ports >= 32768.