Adding cython v0.20.2 in third-party.

third_party/cython/src/Cython/Includes/cpython/version.pxd

+# Python version constants
+#
+# It's better to evaluate these at runtime (i.e. C compile time) using
+#
+#      if PY_MAJOR_VERSION >= 3:
+#           do_stuff_in_Py3_0_and_later()
+#      if PY_VERSION_HEX >= 0x02050000:
+#           do_stuff_in_Py2_5_and_later()
+#
+# than using the IF/DEF statements, which are evaluated at Cython
+# compile time.  This will keep your C code portable.
+
+
+cdef extern from *:
+    # the complete version, e.g. 0x010502B2 == 1.5.2b2
+    int PY_VERSION_HEX
+
+    # the individual sections as plain numbers
+    int PY_MAJOR_VERSION
+    int PY_MINOR_VERSION
+    int PY_MICRO_VERSION
+    int PY_RELEASE_LEVEL
+    int PY_RELEASE_SERIAL
+
+    # Note: PY_RELEASE_LEVEL is one of
+    #    0xA (alpha)
+    #    0xB (beta)
+    #    0xC (release candidate)
+    #    0xF (final)
+
+    char PY_VERSION[]
+    char PY_PATCHLEVEL_REVISION[]