By Alex Williams  Amy Koppelman had always wanted to be a writer, even after all those years she spent slogging away on a first novel in her closetthe only office space available in her cramped Upper West Side apartment.  It was the closest thing I had to a room of ones own,  she says.  She still wanted to be a writer even after she got turned down by Columbias prestigious masters-of-fine-arts fiction program.  Twice. 