Converts spectral fluence data differential in depth and energy
(spc) into a depth-dose. It also allows for the export of TRiP98 compatible
DDD files. The routine calls AT.SPC.read so if you experience problems,
please check if additional arguments for AT.SPC.read are needed (via '...').
For the DDD format, see M. Kr\"amer's TRiP98 documentation:
http://bio.gsi.de/DOCS/TRiP98BEAM/DOCS/trip98fmtddd.html.