move language_level Cython setting to setup.py

as suggested by tacaswell in gh-451

Author: grlee77

pywt/_extensions/_cwt.pyx

@@ -1,4 +1,4 @@
-#cython: language_level=3, boundscheck=False, wraparound=False
+#cython: boundscheck=False, wraparound=False
 from . cimport common
 from . cimport c_wt
 from .common cimport pywt_index_t, MODE

pywt/_extensions/_dwt.pyx

@@ -1,4 +1,4 @@
-#cython: language_level=3, boundscheck=False, wraparound=False
+#cython: boundscheck=False, wraparound=False
 from . cimport common
 from . cimport c_wt
 from .common cimport pywt_index_t, MODE

pywt/_extensions/_pywt.pyx

@@ -1,4 +1,3 @@
-#cython: language_level=3
 # Copyright (c) 2006-2012 Filip Wasilewski <http://en.ig.ma/>
 # Copyright (c) 2012-2018 The PyWavelets Developers
 #                         <https://github.com/PyWavelets/pywt>

pywt/_extensions/_swt.pyx

@@ -1,4 +1,4 @@
-#cython: language_level=3, boundscheck=False, wraparound=False
+#cython: boundscheck=False, wraparound=False
 from . cimport common
 from . cimport c_wt
 

setup.py

@@ -162,8 +162,7 @@ def get_cython_sources(use_cython):
     for k, v in py_defines.items():
         fd.write('%s = %d\n' % (k, int(v)))
 
-
-cythonize_opts = {}
+cythonize_opts = {'language_level': '3'}
 if os.environ.get("CYTHON_TRACE"):
     cythonize_opts['linetrace'] = True
     cython_macros.append(("CYTHON_TRACE_NOGIL", 1))