Small meta cleanups (#4893)

* Remove the unneeded pytest options from pyproject.toml

* Clean up setup.py from old readthedocs.org workaround

* Removes unused folder

* Simplify list of excluded files in black's configuration

* Fix returned exit codes in `make.ps1`

* Add Sublime's project files to `.gitignore`

* Update the link to Black in README and contributing guidelines

pyproject.toml

@@ -2,22 +2,9 @@
     line-length = 99
     target-version = ['py38']
     include = '\.py$'
-    exclude = '''
+    force-exclude = '''
     /(
-          \.eggs
-        | \.git
-        | \.hg
-        | \.mypy_cache
-        | \.tox
-        | \.venv
-        | _build
-        | buck-out
-        | build
-        | dist
-        | redbot\/vendored
+        redbot\/vendored
     )/
     '''
 
-[tool.pytest.ini_options]
-    minversion = "6.0"
-    addopts = "--import-mode=importlib"