Instead of a single function with variadic arguments, a special enum
type containing which string to request, and a special struct to
contain the request and the result, just use separate functions for
each request, and return a std::string by value. Also change the enum
item string access to just give access to the enum item itself and add
const in a few places as necessary.
The callers of the API function get much clearer this way, and it's
much easier to see which information is used to create certain tooltip
strings.