Proposed patch marks most deprecated functions. Code is rewritten for using non-deprecated functions if possible. Unfortunately some deprecated function still are used in the code and can't be easier replaced. They are left not marked.

* PyEval_ReleaseLock() is used in Python/pystate.c. It can't be replaced with PyEval_ReleaseThread() since the latter don't accept NULL.

* Py_UNICODE (currently an alias of wchar_t) is used in a number of deprecated functions and bridges between deprecated and new APIs. Maybe it can be just replaced with wchar_t.

* Macros PyUnicode_GET_SIZE, PyUnicode_GET_DATA_SIZE, PyUnicode_AS_UNICODE, PyUnicode_AS_DATA, functions PyUnicode_AsUnicode and PyUnicode_AsUnicodeAndSize are used in a number of places. They can't be easily replaced with wchar-based functions since they return a borrowed reference to cached representation.

* PyUnicode_FromUnicode, PyUnicode_EncodeDecimal and PyUnicode_TransformDecimalToASCII are used only in Modules/_testcapimodule.c. I think we should write tests for modern APIs and eliminate tests for deprecated APIs. Or temporary silence compiler warning in test functions.

* _PyUnicode_ToLowercase, _PyUnicode_ToUppercase and corresponding public macros Py_UNICODE_TOLOWER and Py_UNICODE_TOUPPER are used in Modules/_sre.c (this is a bug in regex implementation). The problem is that more modern functions _PyUnicode_ToLowerFull and _PyUnicode_ToUpperFull is a private API.

All these cases needs separate issues.