Addresses issue #765.

Blanket wide to all .c and .h files.  Some files originating from ST are
difficult to deal with (license wise) so it was left out of those.

Also merged modpyb.h, modos.h, modstm.h and modtime.h in stmhal/.

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.

Some functionality is still missing (eg and, or, bit shift), and some
things are buggy (eg subtract).

Done by introducing another factored out helper API in binary.c. This API
can be reused also by array and struct modules.