operator pair throws docca for a loop

```
#include
#include

struct T
{
/** Return the decoded key and value as a pair

This function returns the key and value
as a pair, using the default allocator.
It is designed to allow easy copying
of the range into another container, as
shown below:

@par Example
@code
query_params_view qp = parse_query_params( "a=1&b=2&c=3&d=%34" );

std::map< std::string, std::string > m( qp.begin(), qp.end() );

// m now holds the key value pairs from the query params
@endcode
*/
operator std::pair< std::string const, std::string >() const;
};
```

I think this has something to do with how it calculates the name of the function:
```Error: no ID for constraint linkend: "url.ref.boost__urls__url__params_type__value_type.operator_std__pair_lt__std__string_const,_std__string__gt_".
Error: no ID for constraint linkend: "url.ref.boost__urls__url__params_type__value_type.operator_std__pair_lt__std__string_const,_std__string__gt_".
Error: no ID for constraint linkend: "url.ref.boost__urls__query_params_view__value_type.operator_std__pair_lt__std__string_const,_std__string__gt_".
```

In C++ this function is called `operator std::pair< std::string const, std::string >`