Trim trailing whitespace in all md and yml files (#1329)

* Trim non-significant trailing whitespace, add final newlines to md,yml files

* Add .editorconfig with basic whitespace conventions

.editorconfig

@@ -0,0 +1,8 @@
+# https://editorconfig.org/
+
+[*]
+insert_final_newline = true # ensure all files end with a single newline
+trim_trailing_whitespace = true # attempt to remove trailing whitespace on save
+
+[*.md]
+trim_trailing_whitespace = false # in markdown, "two trailing spaces" is unfortunately meaningful; it means `<br>`