enabled bicubic interpolation

Bicubic interpolation is now working, produces sharper images (tested).
Next step is to perform a series of these interpolations so instead of
one interplation scaling from 40 pixels to 1, we do 5 interpolations
scaling from 8 to 1 (for example). Should retain a better image!
interpolation/naming update

changed the names of some variables and modifying the interpolation to
do many small steps instead of one large one.