fix stdout option for python 2 and 3, add option for remote url

adds ability to convert files with remote input url, 
checks python version before writing to stdout and uses buffered write for python 3 and direct write for earlier versions,
adds stdin option using private:stream

```
root@app0:~# unoconv --version
unoconv 0.6
Written by Dag Wieers <dag@wieers.com>
Homepage at http://dag.wieers.com/home-made/unoconv/

platform posix/linux2
python 2.7.3 (default, Feb 27 2014, 20:00:17)
[GCC 4.6.3]
LibreOffice 4.2
```

```
root@app0:~# unoconv -r --stdout -f html http://fqdn.com/sample.docx
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
...
```