Still some method names to iron out, and funtionality to add, but this
will do for the first, basic version.

Also now returns correct POSIX errno when an IO operation fails.

Addresses issues #516 and #676.

Signed-off-by: Sven Wegener <sven.wegener@stealer.net>

time.time: returns seconds since 1/1/2000, as an integer.

time.localtime: Returns 8-tuple: (year, month, date, hour, minute,
    second, weekday, yearday).

Blanket wide to all .c and .h files.  Some files originating from ST are
difficult to deal with (license wise) so it was left out of those.

Also merged modpyb.h, modos.h, modstm.h and modtime.h in stmhal/.

Instead of pyb.switch() as a function, it's more consistent (with
respect to all the other modules and peripherals) to have
pyb.Switch() create a switch object.  This then generalises to having
multiple switches.  Call the object to get its state.  Use sw.callback
to set the callback function for when the switch is pressed.

It should be a noun, since it supports getting and setting depending on
the number of arguments given.

Simple but functional timer control.  More sophistication will
eventually be added, or for now just use direct register access :)

Also added pyb.freq() function to get MCU clock frequencies.

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.

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

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

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.

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.

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.

Can now calibrate, set pulse width, angle and speed.

They correspond to io.FileIO in io module hierarchy (with small caveat
that io.FileIO is raw file and works with bytes, not strings).

This is to reduce ROM usage.  stream_p is used in file and socket types
only (at the moment), so seems a good idea to make the protocol
functions a pointer instead of the actual structure.

It saves 308 bytes of ROM in the stmhal/ port, 928 in unix/.

This adds readline(), readall(), etc. methods. Also other fixes to make
Python API compliant and "with" support.

Can now choose at boot up whether the USB device is CDC+MSC or CDC+HID.
Choice is made by an option in boot.py, with default being CDC+MSC.
HID+MSC is not currently supported, but should be easy to implement.

Boot up now has ability to change the reset mode: hold down USR switch
while booting and LEDs will count from 1 to 7 to indicate the boot mode.
Release USR when correct mode is selected.  Current modes are 1 (normal
boot), 2 (safe mode), 3 (reset FS mode).

Addresses issue #377.