make select const, use unique_ptr for selector in DiPhotonProducer
Merge pull request #5 from sethzenz/master

make select const, use unique_ptr for selector in DiPhotonProducer
Update README.md
updates for Jets, changed photon interface to return pointers
Merge pull request #6 from sethzenz/master

updates for Jets (in progress), changed photon interface to return pointers