Moved dependencies to setup.py extras (#462)

setup.py

@@ -3,6 +3,19 @@ from setuptools import setup
 with open("README.md", "r") as f:
     long_description = f.read()
 
+test_reqs = [
+    'mock==2.0.0'
+]
+
+doc_reqs = [
+    'Sphinx>=1.5.2'
+]
+
+extra_reqs = {
+    'doc': doc_reqs,
+    'test': test_reqs
+}
+
 setup(
     name='spotipy',
     version='2.10.0',
@@ -16,5 +29,7 @@ setup(
         'requests>=2.20.0',
         'six>=1.10.0',
     ],
+    tests_require=test_reqs,
+    extras_require=extra_reqs,
     license='LICENSE.md',
     packages=['spotipy'])