Use find_packages to populate the package list

This will prevent further issues like google#372 (though technically google#372
would still have caused a problem because __init__.py was missing).

setup.cfg

@@ -22,19 +22,7 @@ classifiers =
 [options]
 python_requires = >=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*, <3.8
 packages =
-    pytype
-    pytype/overlays
-    pytype/pyc
-    pytype/pyi
-    pytype/pytd
-    pytype/pytd/parse
-    pytype/tools
-    pytype/tools/analyze_project
-    pytype/tools/annotate_ast
-    pytype/tools/merge_pyi
-    pytype/tools/traces
-    pytype/tools/xref
-    pytype/typegraph
+    find:
 install_requires =
     attrs
     importlab>=0.5.1
@@ -43,6 +31,15 @@ install_requires =
     six
     typed_ast; python_version >= "3.3"
 
+[options.packages.find]
+include =
+    pytype
+    pytype.*
+exclude =
+    pytype.test_data
+    pytype.tests
+    pytype.typeshed.tests
+
 [options.entry_points]
 console_scripts =
     annotate-ast = pytype.tools.annotate_ast.main:main