message: Small fixes to coord docs.
diff: This introduces some helpers and terminology that are used throughout MiniGo.
  -MiniGo Coord/Coordinate: This is a tuple of the form (column, row) that's
  - indexed from (0,0) from the upper-left.
  +MiniGo Coordinate: This is a tuple of the form (row, column) that is indexed
  + starting out at (0, 0) from the upper-left.
  Flattened Coordinate: this is a number ranging from 0 - N^2 (so N^2+1
  possible values). The extra value N^2 is used to mark a 'pass' move.
  SGF Coordinate: Coordinate used for SGF serialization format. Coordinates use
  - two-letter pairs (r,c) indexed from the upper-left (aa).
  -KGS Coordinate: Human-readable coordinate indexed from bottom left.
  -PYGTP Coordinate: Tuple coordinate indexed starting at 1,1 from top-left (r, c)
  + two-letter pairs (c, r) indexed from the upper-left (aa).
  +KGS Coordinate: Human-readable coordinate string indexed from bottom left, with
  + the first character a capital letter and the second a number from 1-19.
  +PYGTP Coordinate: Tuple coordinate indexed starting at 1,1 from bottom-left
  + in the format (column, row)
  So, for a 19x19,
  