Add .editorconfig.

Author: davidlehn

.editorconfig

@@ -0,0 +1,17 @@
+# http://editorconfig.org
+
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.{js,json,jsonld,yaml,yml}]
+indent_style = space
+indent_size = 2
+
+[*.py]
+indent_style = space
+indent_size = 4