Add .editorconfig

.editorconfig

@@ -0,0 +1,23 @@
+root = true
+
+
+[*]
+indent_style = space
+indent_size = 4
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+
+[Makefile]
+indent_style = tab
+indent_size = unset
+
+# ignore external repositories and test inputs
+[tests/{unity,json-patch-tests,inputs}/*]
+indent_style = unset
+indent_size = unset
+end_of_line = unset
+charset = unset
+trim_trailing_whitespace = unset
+insert_final_newline = unset