added new tests to cross_correlation_shifts, along with some docs
added new tests to cross_correlation_shifts, along with some docs

jcesardasilva/agpy,ufoym/agpy,tectronics/agpy,tectronics/agpy,ufoym/agpy,Leotrinos/agpy,ufoym/agpy,tectronics/agpy,Leotrinos/agpy,tectronics/agpy,jcesardasilva/agpy,Leotrinos/agpy,jcesardasilva/agpy,ufoym/agpy,Leotrinos/agpy,jcesardasilva/agpy