List available icons using --list fails
I am using the current version, installed via pip.

Downloading the font using:

`icon-font-to-png --download font-awesome`

worked without issues - as a result i got the .css and the .ttf file.

But if i try to list all icons using:

`icon-font-to-png --css font-awesome.css --ttf fontawesome-webfont.ttf --list`

i get no output at all.

