Marker type for SQL names

How do you quote and escape SQL identifiers for inclusion into a query? Think table names, column names, that kind of thing.

Right now, you do that by calling quote_name() on your connection or transaction. For actual values you use quote() instead.

I'd like to introduce a marker type which tells libpqxx "this string is an identifier in SQL." You call the regular quote() on that, and the type of the argument will tell libpqxx which quoting rules it should apply.

That will also make it easier to add a new form of the quote() function, where you provide the buffer for the resulting text. That may help us avoid some memory allocations, and improve performance.