Feature add keep 730 (#740)

* Implemented #730, --keep

* Implemented #739, fixed --keep to accept relative paths

* Updated to macos-latest

Ref: https://github.com/actions/virtual-environments/issues/5583

* Release files for #730

docs/_static/documentation_options.js

@@ -1,6 +1,6 @@
 var DOCUMENTATION_OPTIONS = {
     URL_ROOT: document.getElementById("documentation_options").getAttribute('data-url_root'),
-    VERSION: '0.50.9',
+    VERSION: '0.50.10',
     LANGUAGE: 'None',
     COLLAPSE_INDEX: false,
     BUILDER: 'html',