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.

Reads ADC values into a bytearray (or similar) at a fixed rate.  Needs a
better name and improved API.  Also fix up DAC dma function (which also
needs a better name and API).

Simple way to find the address of an attached I2C device.

Packets of 64 bytes length are not send to the host until the following
packet is sent.  Fixed by never sending packets of 64 bytes length.

Available via sys.std{in,out,err}.  Basic reading and writing supported.
Even sys.stdin.readline!

Should address issue #475.

Must use mp_obj_get_type to get the type of an object.  Can't assume
mp_obj_t is castable to mp_obj_base_t.

Pass a single parameter (doesn't matter what): pyb.info(1), will dump
the GC alloc table.

Also contains raw memory read/write functions, read8, read16, read32,
write8, write16, write32.  Can now do:

stm.write16(stm.GPIOA + stm.GPIO_BSRRL, 1 << 13)

This turns on the red LED.

With the new constant folding, the above constants for the GPIO address
are actually compiled to constants (and the addition done) at compile
time.  For viper code and inline assembler, this optimisation will make
a big difference.  In the inline assembler, using these constants would
not be possible without this constant folding.