Added tox.ini configuration

tox.ini

@@ -0,0 +1,35 @@
+[tox]
+envlist = py{36,37,38}-{test,docs}
+requires = pip >= 18.0
+           setuptools >= 30.3.0
+
+[testenv]
+passenv =
+    DISPLAY
+    HOME
+setenv =
+    CI = true
+changedir =
+    docs: docs
+deps:
+    PyQt5==5.9.*
+    test: pyopengl
+extras =
+    test: test,lab
+    docs: docs
+commands =
+    test: pip freeze
+    test: python -c 'import pywwt'
+    test: jupyter nbextension list
+    test: jupyter labextension list
+    test: jupyter serverextension list
+    test: python .check_enabled.py
+    test: pytest pywwt --cov pywwt -p no:warnings {posargs}
+    docs: sphinx-build -n -b html -d _build/doctrees   . _build/html
+    docs: sphinx-build -n -b linkcheck -d _build/doctrees   . _build/html
+
+[testenv:codestyle]
+deps = flake8
+skip_install = true
+commands =
+    flake8 --max-line-length=200 pywwt