With minor changes to adc.c and storage.c to support the F769.

The temperature sensor on F4 and F7 MCUs is mostly, but not always, on
channel 16.  To retain compatibility across all these MCUs this patch
maps the user-facing channel 16 to the internal temperature sensor.

It now uses factory calibration values to get a more accurate value, and
returns a float instead of an integer.

By using factory calibration values.

The "mask" parameter is used to select which pins the ADCAll constructor
will initialise to analog mode.  It defaults to all pins (0xffffffff),
which is backwards compatible with previous behaviour.

Fixing Issue #2243. Main problems were:

- HAL_ADC_GetState(adcHandle) may return other bits set (not only
  HAL_ADC_STATE_EOC_REG) when called - so I AND-ed it out as proposed by
  mattbrejza in Issue #2243.
- ADC Pin has to be configured as GPIO_MODE_ANALOG_ADC_CONTROL not only
  GPIO_MODE_ANALOG.
- Resolved ADC resolution L4 specific (Use L4 define ADC_RESOLUTION_12B).
- Changed setting of Init.EOCSelection toADC_EOC_SINGLE_CONV for L4.
- Added call to ADC_MultiModeTypeDef as this is done on a STM32Cube
  generated project too.
- Clean up: Configuration of ADC is done only in ONE function not the same
  is done in two functions.

Test is done on PA5 pin of STM32L4Discovery-Kit which is connected to the
DOWN button.

Thanks to mattbrejza for discovering the bug.

The first argument to the type.make_new method is naturally a uPy type,
and all uses of this argument cast it directly to a pointer to a type
structure.  So it makes sense to just have it a pointer to a type from
the very beginning (and a const pointer at that).  This patch makes
such a change, and removes all unnecessary casting to/from mp_obj_t.

py/mphal.h contains declarations for generic mp_hal_XXX functions, such
as stdio and delay/ticks, which ports should provide definitions for.  A
port will also provide mphalport.h with further HAL declarations.

Extracted GPIO clock enable logic into mp_hal_gpio_clock_enable
and called from anyplace which might need to use GPIO functions
on ports other than A-D.

Thanks to Dave Hylands for the patch.

This allows a user-specified Timer for the triggering of the ADC read,
mirroring the new behaviour of DAC.write_timed.

Addresses issue #1129.

Fixes sign-compare warning.

Saves 68 bytes.

Previous to this patch the printing mechanism was a bit of a tangled
mess.  This patch attempts to consolidate printing into one interface.

All (non-debug) printing now uses the mp_print* family of functions,
mainly mp_printf.  All these functions take an mp_print_t structure as
their first argument, and this structure defines the printing backend
through the "print_strn" function of said structure.

Printing from the uPy core can reach the platform-defined print code via
two paths: either through mp_sys_stdout_obj (defined pert port) in
conjunction with mp_stream_write; or through the mp_plat_print structure
which uses the MP_PLAT_PRINT_STRN macro to define how string are printed
on the platform.  The former is only used when MICROPY_PY_IO is defined.

With this new scheme printing is generally more efficient (less layers
to go through, less arguments to pass), and, given an mp_print_t*
structure, one can call mp_print_str for efficiency instead of
mp_printf("%s", ...).  Code size is also reduced by around 200 bytes on
Thumb2 archs.

Addresses issue #1154.

There was a stray factor of 2 (VBAT_DIV) that looks like it was copied incorrectly from the read_core_vbat() function.
The factor exists in read_core_vbat() because VBAT is measured through a 2:1 voltage divider.
read_core_vref now returns values around 1.21V (assuming that external reference voltage is 3.3V) which is in line with the datasheet values.
See comment at http://forum.micropython.org/viewtopic.php?f=6&t=533&p=2991#p2991

Teensy doesn't need to worry about overflows since all of
its timers are only 16-bit.

For PWM, the pulse width needs to be able to vary from 0..period+1
(pulse-width == period+1 corresponds to 100% PWM)

I couldn't test the 0xffffffff cases since we can't currently get a
period that big in python. With a prescaler of 0, that corresponds
to a freq of 0.039 (i.e. cycle every 25.56 seconds), and we can't
set that using freq or period.

I also tested both stmhal and teensy with floats disabled, which
required a few other code changes to compile.

Addressing issue #50, still some way to go yet.

Based on forum post: http://forum.micropython.org/viewtopic.php?f=6&t=193

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/.

Decided to write own script to pull documentation from comments in C code.
Style for writing auto generated documentation is: start line with ///
and then use standard markdown to write the comment.  Keywords
recognised by the scraper begin with backslash.  See code for examples.

Running: python gendoc.py modpyb.c accel.c adc.c dac.c extint.c i2c.c
led.c pin.c rng.c servo.c spi.c uart.c usrsw.c, will generate a HTML
structure in gendoc-out/.

gendoc.py is crude but functional.  Needed something quick, and this was
it.

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

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.

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