Print current selections, or entire file if not selected. Also, allow different colour schemes

Just a little changing stuff around to let people select regions to print, instead of the entire file. Allows people to print multiple regions at the same time, and they'll appear underneath each other.

I also removed the convert_with_pygments function, as I don't think it's useful to us with these changes.

I also added a simple style setting, that defines which pygments style to use when laying out text. Not sure if I should put it into another Pull Request somehow, it kinda just added it to this one instead.