Move flake8 into src

This is an emerging best practice and there is little reason to not
follow it

setup.py

@@ -3,10 +3,13 @@
 from __future__ import with_statement
 
 import functools
+import os
 import sys
 
 import setuptools
 
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), 'src'))
+
 import flake8  # noqa
 
 try:
@@ -66,6 +69,7 @@ setuptools.setup(
     maintainer="Ian Cordasco",
     maintainer_email="graffatcolmingov@gmail.com",
     url="https://gitlab.com/pycqa/flake8",
+    package_dir={"": "src"},
     packages=[
         "flake8",
         "flake8.api",

tests/unit/test_utils.py

@@ -71,15 +71,15 @@ def test_fnmatch_returns_the_default_with_empty_default():
 
 def test_filenames_from_a_directory():
     """Verify that filenames_from walks a directory."""
-    filenames = list(utils.filenames_from('flake8/'))
+    filenames = list(utils.filenames_from('src/flake8/'))
     assert len(filenames) > 2
-    assert 'flake8/__init__.py' in filenames
+    assert 'src/flake8/__init__.py' in filenames
 
 
 def test_filenames_from_a_directory_with_a_predicate():
     """Verify that predicates filter filenames_from."""
     filenames = list(utils.filenames_from(
-        arg='flake8/',
+        arg='src/flake8/',
         predicate=lambda filename: filename == 'flake8/__init__.py',
     ))
     assert len(filenames) > 2

tox.ini

@@ -24,7 +24,7 @@ deps =
     flake8-docstrings>=0.2.7
     flake8-import-order
 commands =
-    flake8
+    flake8 src/flake8/ tests/ setup.py
 
 [testenv:pylint]
 basepython = python3