VERITAS test DL3 data set for gammapy development

Test dataset at DL3 level from VERITAS observations to be used for testing and developing the gammapy software. The dataset includes multiple observation runs targeting the Crab Nebula (runs 64080-64083) and the Segue 1 dwarf spheroidal galaxy (runs 73266, 77021, 80190, 81437). Released under an informal data-sharing agreement between the VERITAS collaboration and the Gammapy developer team. For background regarding the VERITAS gamma-ray observatory, visit: https://veritas.sao.arizona.edu/