Added partial geometry extraction to npdet_to_step.
This requires a modified version of ROOT's geocad library. You can find it at https://github.com/whit2333/root/tree/geocad_improvements Features: - 'npdet_to_step list compact.xml' This will print names of level 1 volumes. This is useful for the part selection. - 'npdet_to_step part -l 3 EcalBarrel -o EcalBarrel.stp compact.xml' This will select only the EcalBarrel geometry and output a new STEP file. The Geomtry will only be output up to and include level 3. - These commands can be added together: 'npdet_to_step part -l 3 EcalBarrel \ part -l 2 HcalBarrel \ part -l 4 SiVertexEndcap \ -o det_parts.stp compact.xml' - See 'npdet_to_step help'