item.item_vars["lets_you_save"] = "arbritrary stringified data";
This uses item tags: on load, any tag starting with ascii 001 (^A) is instead
used to populate std::map<std::string, std::string> item_vars, as so:
"^AvariableName=string" => item.item_vars["variableName"] = "string";
Spaces, line feeds, and tabs are escaped as ^A + hex: ^A0D, ^A20, etc.

e are saved and loaded as special item tags that begin with ascii 001 (^A)
item_var comment cleanup
Persistent item state tags.