Support for whitespace symbols in the words.dict file

[ernestum]

If you do character-wise prediction and not word-wise prediction, you might want to predict whitespaces. But the way the words.dict file is parsed right now crashes on whitespaces. This pull request should fix this.

[HendrikStrobelt]

Thanks for adding this. I will merge it.
As best practice we recommend to encode white-spaces as extra word like '<space>' or '__' etc.

[ernestum]

Cool thanks! I thought about that solution too, but only after I implemented the fix.