Thanks to Henrik Sölver for this patch.

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.

When setting usb_mode to "HID", hid config object now has
polling-interval (in ms) as the 4th element.  It mmust now be a 5-tuple
of the form:

(subclass, protocol, max_packet_len, polling_interval, report_desc)

The mouse and keyboard defaults have polling interval at 8ms.

There are lots of cosmetic changes, but this release brings a  very
important bug fix:
 - Fixed f_unlink() does not remove cluster chain of the file.

With R0.10c if you try to write a file that is too large to fit in the
free space of the drive, the operation fails, you delete the incomplete
file, and it seems to be erased, but the space is not really freed,
because any subsequent write operations fail because the drive is
"still" full. The only way to recover from this is by formatting the
drive. I can confirm that R0.11 fixes the problem.

To have proper low power mode, need to configure all unused pins in
input mode, so need to have them available.

This can get PYBv1.0 stop current down to around 290uA.

This also cleans up spurious interrupts which happen at timer
initilaization time.

Disabled by default.  Enabled on unix and stmhal ports.

Given that there's already support for "fixed table" maps, which are
essentially ordered maps, the implementation of OrderedDict just extends
"fixed table" maps by adding an "is ordered" flag and add/remove
operations, and reuses 95% of objdict code, just making methods tolerant
to both dict and OrderedDict.

Some things are missing so far, like CPython-compatible repr and comparison.

OrderedDict is Disabled by default; enabled on unix and stmhal ports.

Most boards (except the pyboard) don't have a 32kHz crystal so they
should use the LSI for the RTC.

This allows to wake from low-power modes at a regular interval.

This method is preliminary, pending testing and API overhaul.

These allow to fine-tune the compiler to select whether it optimises
tuple assignments of the form a, b = c, d and a, b, c = d, e, f.
Sensible defaults are provided.

Addresses issue #1154.

This helps make files reusable across other ports.

This is so all memory requests go through the same interface.

In particular, make sure that the globals are all initialized
before enabling the interrupt, and also make sure that the timer
interrupt has been initialied before enabling the NVIC.

The implementation of these functions is very large (order 4k) and they
are rarely used, so we don't enable them by default.

They are however enabled in stmhal and unix, since we have the room.