Python 3.10 requires PY_SSIZE_T_CLEAN macro in # format

[arimakai]

Dear,

I found error in python3.10

SystemError: PY_SSIZE_T_CLEAN macro must be defined for '#' formats

Reference by this
https://peps.python.org/pep-0353/
https://bugs.python.org/issue40943

After I add

#define PY_SSIZE_T_CLEAN 1

In the first line of 'src/pyi2c.c,' the library can work. Could you please review the source code again to ensure that other variables are also working fine?