Parameter names in auto-generated docs for builtin symbols

The autogenerated docs for built-in symbols currently just have a line number. In certain cases (at least when it's easy) it would be great to include the parameter names from a function declaration. There are hard cases, such as when a function has multiple parameters and doesn't use the same name each time -- or even pattern matches so there is no name for the overall parameter. It's okay to skip these (except for tuples, of course).