Line now uses new style methods - not ready to merge yet

Hi all,

This one was pretty straight forward, no problems. It did highlight for me the value of getting instance variables for styles since I changed a bunch of instance variable calls to method calls which look up style (I'll point that out in-line).

I also removed the `gui_opts` because it doesn't look like we're using those. I'll point that out in-line too.
Agreed that might be suboptimal to call that more than once unnecessarily.

Maybe you could get around it by having a private method on the class that allows us to pass either `x2`, `y2` or both, sets the ivars and calls `enclosing_box_of_line` once at the end. Then `x2=` and `y2=` could be implemented in terms of that private method (as could the various other multiple-assignment call sites).