Add an optioanl dependency on maxminddb

Author: oschwald

setup.py

@@ -36,7 +36,8 @@
     package_dir={'geoip2': 'geoip2'},
     include_package_data=True,
     install_requires=requirements,
-    test_requires=['httpretty>=0.6.1'],
+    extras_require={'Database Reader': ['maxminddb']},
+    tests_require=['httpretty>=0.6.1'],
     test_suite="tests",
     license=open('LICENSE').read(),
     classifiers=(