To be used for peripherals (like radio) that must be location aware.

Enable it via MICROPY_HW_ENABLE_MMCARD.

For consistency with the majority of other MICROPY_HW_ENABLE_xxx macros.

With this and previous patches the stm32 port can now be compiled using
object representation D (nan boxing).  Note that native code and frozen mpy
files with float constants are currently not supported with this object
representation.

The documentation (including the examples) for elapsed_millis and
elapsed_micros can be found in docs/library/pyb.rst so doesn't need to be
written in full in the source code.

When disabled, the pyb.I2C class saves around 8k of code space and 172
bytes of RAM.  The same functionality is now available in machine.I2C
(for F4 and F7 MCUs).

It is still enabled by default.

This is enabled by default.  When it is disabled all legacy functions and
classes in the pyb module are excluded from the build.

The new option is MICROPY_HW_ENABLE_ADC and is enabled by default.

This patch allows to completely compile-out support for USB, and no-USB is
now the default.  If a board wants to enable USB it should define:

    #define MICROPY_HW_ENABLE_USB (1)

And then one or more of the following to select the USB PHY:

    #define MICROPY_HW_USB_FS (1)
    #define MICROPY_HW_USB_HS (1)
    #define MICROPY_HW_USB_HS_IN_FS (1)

This patch adds in internal config value MICROPY_HW_ENABLE_HW_I2C that is
automatically configured, and enabled only if one or more hardware I2C
ports are defined in the mpconfigboard.h file.  If none are defined then
the pyb.I2C class is excluded from the build, along with all supporting
code.  The machine.I2C class will still be available for software I2C.

Disabling all hardware I2C on an F4 board saves around 10,000 bytes of code
and 200 bytes of RAM.

The legacy function pyb.repl_uart() is still provided and retains its
original behaviour (it only accepts a UART object).  uos.dupterm() will now
accept any object with write/readinto methods.  At the moment there is just
1 dupterm slot.

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.

The renames are:
HAL_Delay -> mp_hal_delay_ms
sys_tick_udelay -> mp_hal_delay_us
sys_tick_get_microseconds -> mp_hal_ticks_us

And mp_hal_ticks_ms is added to provide the full set of timing functions.

Also, a separate HAL_Delay function is added which differs slightly from
mp_hal_delay_ms and is intended for use only by the ST HAL functions.

This new function controls what happens on a hard-fault:
- debugging disabled: board will do a reset
- debugging enabled: board will print registers and stack and flash LEDs

The default is disabled, ie to do a reset.  This is different to previous
behaviour which flashed the LEDs and waited indefinitely.

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.

In order to have more fine-grained control over how builtin functions are
constructed, the MP_DECLARE_CONST_FUN_OBJ macros are made more specific,
with suffix of _0, _1, _2, _3, _VAR, _VAR_BETEEN or _KW.  These names now
match the MP_DEFINE_CONST_FUN_OBJ macros.

This includes making sure that utime_mphal's sleep_ms() and sleep_us()
don't sleep on negative arguments.

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

You can now create (singleton) objects representing the flash and SD
card, using:

    flash = pyb.Flash()
    sdcard = pyb.SDCard()

These objects provide the block protocol.

Per the previously discussed plan. mount() still stays backward-compatible,
and new mkfs() is rought and takes more args than needed. But is a step
in a forward direction.

Adds a lot of code, makes IRQs a bit less efficient, but is very useful
for debugging.  Usage: pyb.irq_stats() returns a memory view that can be
read and written, eg:

    list(pyb.irq_stats())
    pyb.irq_stats()[0]
    pyb.irq_stats()[0] = 0

The patch provides general IRQ_ENTER() and IRQ_EXIT() macros that can be
modified to provide further IRQ statistics if desired.

pyb.repl_uart still exists but points to os.dupterm.

pyb module still has pyb.delay and pyb.udelay, but these now point to
time.sleep_ms and time.sleep_us respectively.