Added benchmark for gravmag.sphere
Added benchmark for gravmag.sphere

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