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.

Only MASTER mode is supported. Transfer width is configurable to
8, 16 or 32 bits.

This prevents duplication of objects in the sleep list. Also helps
with reducing the code size by ~100 bytes.

This allows to use the On-Chip retention registers for both the
RTC and to share notification flags between the bootloader and the
application. The two flags being shared right now are the "safe boot"
request and the WDT reset cause. we still have 2 more bits free for
future use.

Supports suspend and hibernate modes. Waking is possible throug GPIO
and WLAN.
The mpcallback class is generic and can be reused by other classes.

Such functions are never used after MicroPython has started, and they
remain in RAM wasting space. Now they are placed in a special section
named "boot" which sits just before the heap, allowing us to extend
the effective heap area up to the new boot section. Right now, this
gives us back ~1K, but in the future, more functions might end up in
there as well.

This helps saving ~300 bytes. Thanks to dpgeorge.

Also improve pybsd, and make it save it's pin configuration.
This is a necessary step towards supporting the CC3200 low
power deep sleep (LPDS) mode.

Use the simplelink wrappers instead. This is one step further
towards having a single module for the cc3200 and the cc3100.

I2C objects can be freed by the GC and a __del__ method is provided
in order to de-init the peripheral prior to being garbage collected.
UART objects are now added to a local list and this list is now part
of the VM_STATE.

Now all ports can use pybstdio.c to provide sys.stdin/stdout/stderr, so
long as they implement mp_hal_stdin_* and mp_hal_stdout_* functions.

The port currently implements support for GPIO, RTC, ExtInt and the WiFi
subsystem. A small file system is available in the serial flash. A
bootloader which makes OTA updates possible, is also part of this initial
implementation.