converts only some white spaces to non-breaking

It's not a proper pr, but kind of work in progress, I would like to know what you think.

For some reason it doesn't work for highlighted code, only plain text (I mean syntax in ST).
But for plain text it seems work.

![pic 2013-05-14 18 02 31](https://f.cloud.github.com/assets/1975298/500958/6c214f3c-bc87-11e2-99f0-f1b9a1fc5f75.png)