Create a W3ADocumentInfo structure

	[[new_doc]] allocates heap space for a new [[W3ADocumentInfo]]
	structure and initializes all fields. It returns a pointer to
	the new structure.

<<*>>=
#include <config.h>
#include <w3a.h>
#include <str.h>

EXPORT W3ADocumentInfo *new_doc(void)
{
    W3ADocumentInfo *d;

    new(d);
    d->url = NULL;
    d->mime_type = NULL;
    d->mime_params = NULL;
    d->title = NULL;
    d->referer = NULL;
    d->status = NULL;
    d->location = NULL;
    d->size = -1;
    return d;
}