Added iterator support for harvester
Added iterator support for harvester

cmeessen/fatiando,fatiando/fatiando,rafaelmds/fatiando,eusoubrasileiro/fatiando,eusoubrasileiro/fatiando_seismic,drandykass/fatiando,mtb-za/fatiando,santis19/fatiando,drandykass/fatiando,santis19/fatiando,mtb-za/fatiando,fatiando/fatiando,rafaelmds/fatiando,eusoubrasileiro/fatiando,cmeessen/fatiando,eusoubrasileiro/fatiando_seismic,victortxa/fatiando,victortxa/fatiando,eusoubrasileiro/fatiando