docs: cleanup (#567)

* fix: support docs/tests extras, simpler RtD install

Use oldest-supported-numpy from SciPy in example

* chore: bump to ubuntu-20.04 images

* fix: move extras to setup so we can do combinations

setup.py

@@ -1,3 +1,31 @@
 from setuptools import setup
 
-setup()
+extras = {
+    "docs": [
+        "mkdocs-include-markdown-plugin==2.1.1",
+        "mkdocs==1.0.4",
+        "pymdown-extensions",
+    ],
+    "test": [
+        "jinja2",
+        "pytest>=4",
+        "pytest-timeout",
+    ],
+    "dev": [
+        "click",
+        "ghapi",
+        "mypy>=0.800",
+        "packaging>=20.8",
+        "pip-tools",
+        "pygithub",
+        "pyyaml",
+        "requests",
+        "rich>=9.6",
+        "typing-extensions",
+    ],
+}
+
+extras["all"] = sum(extras.values(), [])
+extras["dev"] += extras["test"]
+
+setup(extras_require=extras)