Add API Reference to docs

Makefile

@@ -173,6 +173,7 @@ coverage: ## check code coverage quickly with the default Python
 .PHONY: docs
 docs: clean-docs ## generate Sphinx HTML documentation, including API docs
 	cp -r tutorials docs
+	sphinx-apidoc --separate --no-toc -o docs/api/ btb
 	$(MAKE) -C docs html
 
 .PHONY: view-docs