Do not just respect vertical and horizontal but grid

[EagleoutIce]

Currently, the package only checks for the pixel above and below. However it would be nice if either:

• diagonals can be checked as well (above left/north east, ...)
• Patterns can specify custom guards that may access the complete qr code grid (e.g. to allow
  identification of part of the outer "ring" and therefore not draw/draw as ring"...

The second approach seems to be more efficient because we do not have to generate information for tiles that we do not need and that the only indirection is another macro expansion to produce that information. However, when identifying the pattern we know have to perform O(n) checks and can't just use the macro name. Maybe a hybrid.