Changes in pixmap version 0.2-1

  o pixmap():
    - Added arguments bbcent and cellres
    - nrow and ncol default to the respective dimensions of the data
      argument (if present). Hence, pixmap does the expected when
      given a matrix or an array.
    - data is rescaled to [0,1] for rgb and grey, and coerced to positive
      integers for indexed.   
    - col can also be a function like rainbow()

Changes in pixmap version 0.1-2

  o Fixed bugs in plotting, read.pnm and write.pnm which confused
    dimensions (rows versus columns), but together let plots look OK.

