It's really a UART because there is no external clock line (and hence no
synchronous ability, at least in the implementation of this module).
USART should be reserved for a module that has "S"ynchronous capabilities.

Also, UART is shorter and easier to type :)

The three classes I2C, SPI and USART now have a fairly uniform (Python)
API.  All are constructed, initialised and deinitialised in the same
way.  They can have most of their parameters set, using keyword arguments.
All have send and recv (although slightly different with I2C requiring an
address in master mode).  recv can do inplace receiving (ie store the
data in a previously-created bytearray).

It's just polling mode at the moment, but interrupt and DMA would be
nice to add.

The HAL handles for the I2C/SPI objects are rather large, so we don't
want to unnecessarily include them.

Also some updates to compile with latest changes to core py.

It's Light Emitting Diode, so should be LED.

Main reason for expanding buffer protocol API was to support writes to a
buffer in ADC module (see read_timed).  With this change you can now
create an array of arbitrary type and ADC.read_timed will store into
that array in the correct format (byte, int, float).  I wonder though if
all these changes were really worth it to support just this function.
Hopefully this enhanced buffer protocol API (with typecode specified)
will be used elsewhere.

This is an attempt to clean up the Micro Python API on the pyboard.
Gpio functionality is now in the Pin object, which seems more natural.
Constants for MODE and PULL are now in pyb.Pin.  Names of some
classes have been adjusted to conform to CamelCase.  Other
miscellaneous changes and clean up here and there.

On stmhal, computed gotos make the binary about 1k bigger, but makes it
run faster, and we have the room, so why not.  All tests pass on
pyboard using computed gotos.

With this fix, all tests in tests/basics pass on pyboard.

Any generated headers go in $(BUILD)/genhdr/, and are #included as
'genhdr/xxx.h'.

Needs a better solution.

Taken straight from musl and newlib.  License seems compatible with MIT.

A 64-byte packet is now followed by a 0-byte packet if there is nothing
more to send.  This flushes the USB endpoint.

Internal flash used for the filesystem is now written (from the cache)
only after a 5s delay, or when a file is closed, or when the drive is
unmounted from the host.  This delay means that multiple writes can
accumulate in the cache, and leads to less writes to the flash, making
it last longer.

It's implemented by a high-priority interrupt that takes care of flash
erase and write, and flushing the cache.

This is still only an interim solution for the flash filesystem.  It
eventually needs to be replaced with something that uses less RAM for
the cache, something that can use more of the flash, and something that
does proper wear levelling.

The autogenerated header files have been moved about, and an extra
include dir has been added, which means you can give a custom
BUILD=newbuilddir option to make, and everything "just works"

Also tidied up the way the different Makefiles build their include-
directory flags

Need to wait for the low-level USB driver to send the data over the USB
in-endpoint before the buffer can be used again.  This patch adds a
check for this.

The USB VID&PID are automatically extracted from usbd_desc_cdc_msc.c
and inserted into pybcdc_inf.template, ensuring that the same USB
IDs get used everywhere

Mac OS X sends a SCSI command to remove the medium when it unmounts a
drive.  If this command is not honoured, then OS X will automatically
remount the drive, making it impossible to eject.  This patch disables
the USB MSC when the right SCSI command is sent.