Python 3.11 support, or sunsetting status documentation

[econtal]

7 years after the last commit, I'm still using this library!

Unfortunately it doesn't compile in python 3.11. Could you clarify whether the library will be maintained, or if it's being sunset?

I can compile in Python 3.10, but not 3.11:

      choldate/_choldate.c:107:11: error: too few arguments to function ‘PyCode_New’
        107 |           PyCode_New(a, k, l, s, f, code, c, n, v, fv, cell, fn, name, fline, lnos)
            |           ^~~~~~~~~~

and

      choldate/_choldate.c: In function ‘__Pyx_AddTraceback’:
      choldate/_choldate.c:6338:13: error: invalid use of incomplete typedef ‘PyFrameObject’ {aka ‘struct _frame’}
       6338 |     py_frame->f_lineno = py_line;
            |             ^~

[econtal]

Actually it might be related to #7 which is fixed with #8