Prepare pre-commit and black tools

Author: bboe

.pre-commit-config.yaml

@@ -0,0 +1,8 @@
+default_language_version:
+  python: python3.7
+fail_fast: true
+repos:
+  - hooks:
+      - id: black
+    repo: https://github.com/ambv/black
+    rev: stable

pyproject.toml

@@ -0,0 +1,2 @@
+[tool.black]
+line-length = 79

setup.py

@@ -14,6 +14,14 @@
     VERSION = re.search("__version__ = '([^']+)'", fp.read()).group(1)
 
 
+extras_require = {
+    "dev": ["pre-commit"],
+    "lint": ["black", "flake8"],
+    "test": ["pytest"],
+}
+extras_require["dev"] = sorted(set(sum(extras_require.values(), [])))
+
+
 setup(name=PACKAGE_NAME,
       author='Bryce Boe',
       author_email='[email protected]',
@@ -24,6 +32,7 @@
           'Programming Language :: Python :: 3'],
       description='A program to delete old slack messages.',
       entry_points={'console_scripts': ['deslackify = deslackify:main']},
+      extras_require=extras_require,
       install_requires=['slacker >=0.12, <0.13'],
       keywords='slack',
       license='Simplified BSD License',