vfs.h is for generic VFS declarations, and vfs_fat.h is for VfsFat
specific things.

Everyone should now be using the new ooFatFs library.  The old one is no
longer supported and will be removed.

Replaced by MICROPY_VFS and the VFS sub-system.

It can be useful for low-level lookup of paths by ports.

From https://github.com/micropython/oofatfs, branch work-R0.12b,
commit 46fb53331e7a583c29a41d37ce4b53f2718597e5.

A signal is like a pin, but ca also be inverted (active low). As such, it
abstracts properties of various physical devices, like LEDs, buttons,
relays, buzzers, etc. To instantiate a Signal:

pin = machine.Pin(...)
signal = machine.Signal(pin, inverted=True)

signal has the same .value() and __call__() methods as a pin.

For polymorphic interfacing on C level.

Based on the following statistics:

$ git log docs |grep Author | sort | uniq -c | sort -n -r
    175 Author: Paul Sokolovsky
    135 Author: Damien George
     31 Author: Daniel Campora
     26 Author: danicampora
     14 Author: Peter Hinch

git blame stats script from http://stackoverflow.com/a/13687302/496009:

$ sh git-authors docs
   9977 author Damien George
   2679 author Paul Sokolovsky
   1699 author Daniel Campora
   1580 author danicampora
   1286 author Peter Hinch
    282 author Shuning Bian
    249 author Dave Hylands

Total lines per this script: 18417, my contribution is 14.5%.

socket.error is deprecated even in upstream:
https://docs.python.org/3/library/socket.html#socket.error,
and never was a part of MicroPython socket API.

This was apparently of an ::only directive which was later removed.

It's very low, hardware level, with associated constraints on operations
and callbacks.

To enable options which may be incompatible with other boards, etc.

Overriding CONF_FILE in "minimal" target itself is too late due to include-
pinned $(Z_EXPORTS) target.

From https://github.com/micropython/oofatfs, branch work-R0.12b,
commit 1e295b40550664bbaac18d95a4b6a58154464d31.

They disappeared when stmhal changed to use new MICROPY_VFS code.

This patch makes the following configuration changes:
- MICROPY_FSUSERMOUNT is disabled, removing old mounting infrastructure
- MICROPY_VFS is enabled, giving new VFS sub-system
- MICROPY_VFS_FAT is enabled, giving uos.VfsFat type
- MICROPY_FATFS_OO is enabled, to use new ooFatFs lib, R0.12b

User facing API should be almost unchanged.  Most notable changes are
removal of os.mkfs (use os.VfsFat.mkfs instead) and pyb.mount doesn't
allow unmounting by passing None as the device.