Bring back tox.ini

Were adjusted in #299 after them breaking in baf859b but technically
these wouldn't be able to install dependencies.

Author: tony

tox.ini

@@ -1,5 +1,21 @@
 [tox]
-envlist = py27, py33, py34, py35, py36
+isolated_build = True
+envlist = py37, py38, py39, py310
+skip_missing_interpreters = true
 
 [testenv]
-commands = make test []
+extras = 
+        test
+	docs
+allowlist_externals =
+        make
+	poetry
+require_poetry = true
+install_dev_deps = true
+locked_deps = 
+        pytest
+        pytest-cov
+commands = 
+        make test test='{posargs}'
+setenv = 
+        PYTHONPATH = {toxinidir}