make context fields in refnanny context visible from Python code

Cython/Runtime/refnanny.pyx

@@ -15,10 +15,10 @@ LOG_NONE, LOG_ALL = range(2)
 
 @cython.final
 cdef class Context(object):
-    cdef object name, filename
-    cdef dict refs
-    cdef list errors
-    cdef Py_ssize_t start
+    cdef public object name, filename
+    cdef public dict refs
+    cdef public list errors
+    cdef public Py_ssize_t start
 
     def __init__(self, name, line=0, filename=None):
         self.name = name