THis is required to deal well with signals, signals being the closest
analogue of hardware interrupts for POSIX. This is also CPython 3.5
compliant behavior (PEP 475).

The main problem implementing this is to figure out how much time was
spent in waiting so far/how much is remaining. It's well-known fact that
Linux updates select()'s timeout value when returning with EINTR to the
remaining wait time. Here's what POSIX-based standards say about this:
(http://pubs.opengroup.org/onlinepubs/9699919799/functions/pselect.html):

"Upon successful completion, the select() function may modify the object
pointed to by the timeout argument."

I.e. it allows to modify timeout value, but doesn't say how exactly it is
modified. And actually, it allows such modification only "upon successful
completion", which returning with EINTR error hardly is.

POSIX also allows to request automatic EINTR restart for system calls using
sigaction call with SA_RESTART flag, but here's what the same document says
about it:

"If SA_RESTART has been set for the interrupting signal, it is
implementation-defined whether the function restarts or returns with
[EINTR]."

In other words, POSIX doesn't leave room for both portable and efficient
handling of this matter, so the code just allows to manually select
Linux-compatible behavior with MICROPY_SELECT_REMAINING_TIME option,
or otherwise will just raise OSError. When systems with non-Linux behavior
are found, they can be handled separately.

With these you can now do things like:

stm.mem32[0x20000000] = 0x80000000

and read 32-bit values. You can also read all the way to the end
of memory using either stm.mem32[0xfffffffc] or stm.mem32[-4].

IRQs shouldn't use mem32 at all since they'd fail if the top 2 bits
weren't equal, so IRQs should be using 16-bit I/O.

The STMCube examples define both USE_USB_HS and USE_USB_HS_IN_FS when they
use the HS in FS mode.

The STM32F401 doesn't have a USB_HS at all, so the USB_OTG_HS instance
doesn't even exist.

Define MICROPY_NO_ALLOCA=1 and memory will be allocated from heap instead
and freed by garbage collection.

The UARTs have no FIFOs, so if interrupts are disabled
for more than a character time (10 usec at 1 Mbit/sec)
then characters get dropped.

The overhead for handling a UART ISR is about 0.5 usec,
so even at baud rates of 1 Mbit/sec this only corresponds
to about 5% of the CPU. Lower baud rates will have less
of an impact.

Based on vendor API documentation, untested on real hardware.

Unconditionally wait for MicroPython banner. On overloaded systems, when
using emulators, etc. initial executable startup may take more than 20ms.

uwTick can only change in the SysTick IRQ so this IRQ function does not
need to take special care with this variable.  It's important to make
this IRQ function as efficient as possible.

Using SysTick to do the counting and dispatch of the flash storage idle
handler is more efficient than requiring a dedicated hardware timer.
No new counter is needed, just the existing uwTick variable.  The
processing is not actually done in the SysTick IRQ, it is deferred to
the flash IRQ (which runs at lower priority).

This can be generalised if/when more processing is needed by SysTick.

Thanks to @chuckbook for the idea.

- add mp_int_t/mp_uint_t typedefs in mpconfigport.h
- fix integer suffixes/formatting in mpconfig.h and mpz.h
- use MICROPY_NLR_SETJMP=1 in Makefile since the current nlrx64.S
  implementation causes segfaults in gc_free()
- update README

The BSD stuff is a copy from the unix makefile but at least there it
makes some sense, a windows makefile on BSD doesn't.
The -lmman flag is probably for mmap functions but there is no other build
support for it on windows so just that flag won't cut it anyway.

This started out using IgorLektorovEpam work in PR #1389
and reworked it.

Turning on each DMA block increases the current consumption
by about 8 mA. This code adds an idle timer for each DMA
block and turns off the clocks when no streams are in use
for 128 msec. Having a small timeout allows for improved
performance when back-to-back transfers are being performed.

The 128 msec is basically a guess.

- added some comments to explain the priority/sub-priority.
- adds an entry for SDIO (to be used in a later patch)
- increases DMA priority above USB so that DMA can be used
  for sdcard I/O when using USB Mass Storage.

If RTC is already running at boot then it's left alone.  Otherwise, RTC is
started at boot but startup function returns straight away.  RTC startup
is then finished the first time it is used.  Fallback to LSI if LSE fails
to start in a certain time.

Also included:
 MICROPY_HW_CLK_LAST_FREQ
        hold pyb.freq() parameters in RTC backup reg
 MICROPY_HW_RTC_USE_US
        option to present datetime sub-seconds in microseconds
 MICROPY_HW_RTC_USE_CALOUT
        option to enable RTC calibration output

CLK_LAST_FREQ and RTC_USE_CALOUT are enabled for PYBv1.0.

This patch checks that there is only one *, and that ** is last in the
arg list.