Add 'U'/'U#' format characters to Py_BuildValue (and thus

Add 'U'/'U#' format characters to Py_BuildValue (and thus
to PyObject_CallFunction()) that take a char * (and a size
in the case of 'U#') and create a unicode object out of it.

Add functions PyUnicode_FromFormat() and PyUnicode_FromFormatV()
that work similar to PyString_FromFormat(), but create a unicode
object (also a %U format character has been added, that takes
a PyObject *, which must point to a unicode object).

Change the encoding and reason attributes of UnicodeEncodeError,
UnicodeDecodeError and UnicodeTranslateError to be unicode
objects.