DataFrame.from_records should have an optional "size" parameter
Currently, `data` should have a `__len__` method. However in some cases I'd like to pass a iterator with a known size (mostly in the case of database, where I can run the `SELECT SUM(...) FROM table`, for the size. Then `SELECT * FROM table` and pass the cursor as `data`.

Currently I need to create in memory copy of the rows in the cursor.
