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.

Display \r and \t escape codes in string repr

Full CPython compatibility with this requires actually parsing the
input so far collected, and if it fails parsing due to lack of tokens,
then continue collecting input.  It's not worth doing it this way.  Not
having compatibility at this level does not hurt the goals of Micro
Python.