- In Vedeu::XCoordinate and Vedeu::YCoordinate, rename #d_dn to #bd_bdn
- Add new #d_dn to Vedeu::XCoordinate and Vedeu::YCoordinate.
- Rename all private instance variables used for memoization from '@...' to '@_...'.
- Add Vedeu::Index which converts a Vedeu::Point to an array index. i.e. Never less than 0, always 1 less than the Vedeu::Point value.
- Investigate the differences between memoizing in Vedeu::Geometries::Geometry#area and not memoizing. Memoizing saves ~80ms on running test suite and considerably impacts app responsiveness, however changes to the geometry (such as movement or maximising) are not reflected.