Adds tests in MANIFEST.in (ets-labs#204)

Author: Gerschtli

MANIFEST.in

@@ -1,6 +1,8 @@
 recursive-include src/dependency_injector *.py *.pyx *.pxd *.c
+recursive-include tests *.py
 include README.rst
 include CONTRIBUTORS.rst
 include LICENSE.rst
 include requirements.txt
 include setup.py
+include tox.ini