So we can add more flags.

Small reduction in ROM, heap and stack usage.

Convert int types to uint where sensible, and then to uint8_t or
uint16_t where possible to reduce RAM usage.

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

Fix make-pins.py to support having multiple names for a pin.

SW and X17 now both map to PB3

Fixes #449.

With the implementation of proper string formatting, code to print a
small int was delegated to mpz_as_str_inpl (after first converting the
small int to an mpz using stack memory).  But mpz_as_str_inpl allocates
heap memory to do the conversion, so small ints needed heap memory just
to be printed.

This fix has a separate function to print small ints, which does not
allocate heap, and allocates less stack.

String formatting, printf and pfenv are now large beasts, with some
semi-duplicated code.

These two are apprerently the most concise and efficient way to convert
int to/from bytes in Python. The alternatives are struct and array modules,
but methods using them are more verbose in Python code and less efficient
in memory/cycles.

This makes the runtime and object APIs more consistent.  mp_store_subscr
functionality now moved into objects (ie list and dict store_item).

At this point, all opcodes are now implemented!

Some del opcodes have been combined with store opcodes, with the value
to store being MP_OBJ_NULL.

To create bytearray of given length.

If no nlr_buf has been pushed, and an nlr_jump is called, then control
is transferred to nlr_jump_fail (which should bail out with a fatal
error).

To keep it maintainable, windows port now uses as much as possible from
unix port.  Maybe could even use mpconfigport.h.