Evaluated Pion Photoproduction Cross Section Data Directory

Mattione ea PhysRevC96:035204,2017
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Authors: A.Afanasev, W.Briscoe, and I.Strakovsky
        (revison 15 February 2018)

Evaluated cross section data for pion photoproduction

-- gp_pi0p.dat - gp-->pi0p
-- gp_pi+n.dat - gp-->pi+n
-- gn_pi-p.dat - gn-->pi-p
-- gn_pi0n.dat - gn-->pi0n

Add data format is G4VPhysicsVector compatible

Kinetic energy in MeV and cross section in microbarns
