Add .editorconfig

Had some issues with my editor trying to convert tab-indented files to
spaces, this resolves that.

.editorconfig

@@ -0,0 +1,22 @@
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+indent_size = 2
+indent_style = tab
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.rb]
+indent_style = space
+
+[*.py]
+indent_style = space
+indent_size = 4
+
+[_testdata/**]
+charset = unset
+indent_size = unset
+indent_style = unset
+trim_trailing_whitespace = unset