Add a code formatting tool chain

- (auto-)format code with:
  + autoflake => * remove unused imports and variables
                 * remove duplicate dict keys
                 * expand star imports
  + black => enforce an uncompromising code style
  + isort => enforce a consistent import style
             (complying with Google's Python Style Guide)
- implement the nox session "format" that runs all these tools
- add the following file:
  + setup.cfg => holds configurations for the develop tools

pyproject.toml

@@ -2,6 +2,11 @@
 build-backend = "poetry.masonry.api"
 requires = ["poetry>=0.12"]
 
+[tool.black]
+line-length = 88
+skip-string-normalization = true
+target-version = ["py38"]
+
 [tool.poetry]
 name = "urban-meal-delivery"
 version = "0.1.0.dev0"
@@ -25,3 +30,8 @@ python = "^3.8"
 [tool.poetry.dev-dependencies]
 # Task Runners
 nox = "^2020.5.24"
+
+# Code Formatters
+autoflake = "^1.3.1"
+black = "^19.10b0"
+isort = "^5.2.2"