Fixed issue #4 and #5

Issue #4: the dump option failed completely.

```
(venv)[2013-01-04 11:07:03] pavel@addison:~/projects/epub
# ./epub.py -d ~/novel.epub
A Novel
-------




Traceback (most recent call last):
  File "./epub.py", line 362, in <module>
    dump_epub(args.EPUB)
  File "./epub.py", line 178, in dump_epub
    maxcol=screen.getmaxyx()[1]
NameError: global name 'screen' is not defined
(venv)[2013-01-04 11:07:11] pavel@addison:~/projects/epub
```

Issue #5: there was no way to wrap to anything other than 72 columns.