[Halld-offline] extract_ptype_hddm tool available

[David Lawrence]

Hi All,

     I have just committed a new tool that can be used to extract 
generated particles of a specific type from the input source and write 
them as single events to a new HDDM file.

     This is motivated by my desire to have a sample of generated 
neutrons that matches the full background spectrum produced by bggen 
(pythia), but as clean, single particle events.

     The tool is in the form of a plugin which can be found here:

sim-recon/src/programs/Simulation/plugins/extract_ptype_hddm

There is a README file that gives some details on usage.

Regards,
-David