Add pre-commit config and apply changes (#54)

- Add .pre-commit-config.yaml with initial config.
- Add python black pre-commit config
- Apply pre-commit code changes
- Add information to CONTRIBUTING.md
- Add pre-commit to build requirements
- Run pre-commit during travis CI build
- Use a travis build matrix to control when pre-commit runs
  in the CI process. Use explicit include to only run
  pre-commit on Python 3.9.

build_examples.py

@@ -1,15 +1,23 @@
 import anybadge
 
-if __name__ == '__main__':
+if __name__ == "__main__":
 
-    print("""| Color Name | Hex Code | Example |
-    | ---------- | -------- | ------- |""")
+    print(
+        """| Color Name | Hex Code | Example |
+    | ---------- | -------- | ------- |"""
+    )
     for color, hex in sorted(anybadge.COLORS.items()):
 
-        file = 'examples/color_' + color + '.svg'
+        file = "examples/color_" + color + ".svg"
 
-        url = 'https://cdn.rawgit.com/jongracecox/anybadge/master/' + file
+        url = "https://cdn.rawgit.com/jongracecox/anybadge/master/" + file
 
-        anybadge.Badge(label='Color', value=color, default_color=color).write_badge(file, overwrite=True)
+        anybadge.Badge(label="Color", value=color, default_color=color).write_badge(
+            file, overwrite=True
+        )
 
-        print("| {color} | {hex} | ![]({url}) |".format(color=color, hex=hex.upper(), url=url))
+        print(
+            "| {color} | {hex} | ![]({url}) |".format(
+                color=color, hex=hex.upper(), url=url
+            )
+        )