> (Right now) write an exhaustive list of all deprecated APIs: functions, constants, types, etc.

I searched "4.0" in the documentation:

* Py_UNICODE type
* array.array: "u" type
* PyArg_ParseTuple, Py_BuildValue: "u", "u#", "Z", "Z#" formats

* PyUnicode_FromUnicode()
* PyUnicode_GetSize(), PyUnicode_GET_SIZE()
* PyUnicode_AsUnicode(), PyUnicode_AS_UNICODE(), PyUnicode_AS_DATA()
* PyUnicode_AsUnicodeAndSize()
* PyUnicode_AsUnicodeCopy()

* PyUnicode_FromObject()
* PyLong_FromUnicode()
* PyUnicode_TransformDecimalToASCII()

* PyUnicode_Encode()
* PyUnicode_EncodeUTF7()
* PyUnicode_EncodeUTF8()
* PyUnicode_EncodeUTF32()
* PyUnicode_EncodeUTF16()
* PyUnicode_EncodeUnicodeEscape()
* PyUnicode_EncodeRawUnicodeEscape()
* PyUnicode_EncodeLatin1()
* PyUnicode_EncodeASCII()
* PyUnicode_EncodeMBCS()
* PyUnicode_EncodeCharmap()
* PyUnicode_TranslateCharmap()