Modernize extension

- update dependencies
- use tox for testing
- use type hints
- use pathlib and ipaddress from standard library instead of path and
  ipcalc
- fix Sphinx deprecation warnings

Pipfile

@@ -6,12 +6,11 @@ verify_ssl = true
 [dev-packages]
 coverage = "*"
 twine = "*"
-path = "*"
 pytest = "*"
+tox = "*"
+black = "*"
 
 [packages]
 jandd-sphinxext-ip = { path = ".", editable = true }
-Sphinx = ">=4"
+Sphinx = ">=5"
 docutils = "*"
-six = "*"
-ipcalc = ">=1.99"