add dependabot config, clean up rollup, other tiny tweaks

.editorconfig

@@ -0,0 +1,17 @@
+# http://editorconfig.org
+
+# this file is the top-most editorconfig file
+root = true
+
+# all files
+[*]
+charset = utf-8
+end_of_line = lf
+indent_style = space
+indent_size = 2
+trim_trailing_whitespace = true
+insert_final_newline = true
+
+# site content
+[*.md]
+trim_trailing_whitespace = false