use jaconv instead of jcconv for japanese chars

jaconv is available for more Python-versions and seems to be more
professional. Apart from that I added jaconv to the test-requirements
but not the requirements. (If the katakana-stuff really works we can
later add it as a real dependency)

setup.py

@@ -118,7 +118,7 @@ setup(
     setup_requires=[
         'setuptools_scm',
     ],
-    tests_require=['tox', 'pytest', 'pytest-cov', 'pytest-mock', 'nose', 'scripttest', 'mock', 'hypothesis'],
+    tests_require=['jaconv', 'tox', 'pytest', 'pytest-cov', 'pytest-mock', 'nose', 'scripttest', 'mock', 'hypothesis'],
     cmdclass={'test': Tox},
     entry_points={
         'console_scripts': [