Add an example plugin project to source tree

example-plugin/setup.py

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+# -*- coding: utf-8 -*-
+import setuptools
+
+setuptools.setup(
+    name='flake8-example-plugin',
+    license='MIT',
+    version='1.0.0',
+    description='Example plugin to Flake8',
+    author='Ian Cordasco',
+    author_email='graffatcolmingov@gmail.com',
+    url='https://gitlab.com/pycqa/flake8',
+    package_dir={'': 'src/'},
+    packages=['flake8_example_plugin'],
+    entry_points={
+        'flake8.extension': [
+            'X1 = flake8_example_plugin:ExampleOne',
+            'X2 = flake8_example_plugin:ExampleTwo',
+        ],
+    },
+    classifiers=[
+        'Framework :: Flake8',
+        'License :: OSI Approved :: MIT License',
+        'Programming Language :: Python',
+        'Programming Language :: Python :: 2',
+        'Programming Language :: Python :: 2.7',
+        'Programming Language :: Python :: 3',
+        'Programming Language :: Python :: 3.4',
+        'Programming Language :: Python :: 3.5',
+        'Topic :: Software Development :: Libraries :: Python Modules',
+        'Topic :: Software Development :: Quality Assurance',
+    ],
+)

example-plugin/src/flake8_example_plugin/__init__.py

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+"""Module for an example Flake8 plugin."""
+
+from .on_by_default import ExampleOne
+from .off_by_default import ExampleTwo
+
+__all__ = (
+    'ExampleOne',
+    'ExampleTwo',
+)

example-plugin/src/flake8_example_plugin/off_by_default.py

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+"""Our first example plugin."""
+
+
+class ExampleTwo(object):
+    """Second Example Plugin."""
+    name = 'off-by-default-example-plugin'
+    version = '1.0.0'
+
+    off_by_default = True
+
+    def __init__(self, tree):
+        self.tree = tree
+
+    def run(self):
+        """Do nothing."""
+        yield (1, 0, 'X200 The off-by-default plugin was enabled',
+               'OffByDefaultPlugin')

example-plugin/src/flake8_example_plugin/on_by_default.py

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+"""Our first example plugin."""
+
+
+class ExampleOne(object):
+    """First Example Plugin."""
+    name = 'on-by-default-example-plugin'
+    version = '1.0.0'
+
+    def __init__(self, tree):
+        self.tree = tree
+
+    def run(self):
+        """Do nothing."""
+        for message in []:
+            yield message