harvester refactor: added docstrings for data classes
harvester refactor: added docstrings for data classes

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