stk::rectangle

Hi team,
I have just looked at the changes darren commited today, and have found 
out that rectangle contains virtual functions, do you guys really think 
thats good? Imo we should create rectangle_interface class or something 
to derive from, and not use the regular rectangle. These changes make 
rectangle easyli a few 100 bytes(!!!) Big, this is really not the right 
thing to do for an object which the user expects to be lightweight is 
it? Imo we only got two options, either we stop deriving from rectangle, 
or we create two rectangle classes, one which serves as an interface and 
from which you can derive, so it behaves like a rectangle but isnt one, 
but we really shouldnt continue with using a struct full of virtual 
functions everywhere in the code, this is a major source of bloat!