Tile surface sprite sub-block
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In several game blocks you can find a set of sprite for the ground. Below is
the layout of such a sub-block.
Note that the sprites should look to the north (thus, the sprite at 4 has its
back corner up).

The suffix is added to denote a specific sprite in a sequence inside another block.

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Offset  Length  Version  Suffix  Description
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   0       4      1-     #       Flat surface tile.
   4       4      1-     #n      North corner up.
   8       4      1-     #e      East corner up.
  12       4      1-     #ne     North, east corners up.
  16       4      1-     #s      South corner up.
  20       4      1-     #ns     North, south corners up.
  24       4      1-     #es     East, south corners up.
  28       4      1-     #nes    North, east, south corners up.
  32       4      1-     #w      West corner up.
  36       4      1-     #nw     West, north corners up.
  40       4      1-     #ew     West, east corners up.
  44       4      1-     #new    West, north, east corners up.
  48       4      1-     #sw     West, south corners up.
  52       4      1-     #nsw    West, north, south corners up.
  56       4      1-     #esw    West, east, south corners up.
  60       4      1-     #Nb     Steep north slope (bottom part).
  64       4      1-     #Eb     Steep east slope  (bottom part).
  68       4      1-     #Sb     Steep south slope (bottom part).
  72       4      1-     #Wb     Steep west slope  (bottom part).
  76       4      2-     #Nt     Steep north slope (top part).
  80       4      2-     #Et     Steep east slope  (top part).
  84       4      2-     #St     Steep south slope (top part).
  88       4      2-     #Wt     Steep west slope  (top part).
  92                             Total length of the sub-block.
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