The Lyman Continuum Escape Survey: Ionizing Radiation from [O iii]-strong Sources at a Redshift of 3.1

European Research Council (ERC) under the European Union [669253]; Maureen and John Hendricks Visiting Professorship at the Institute for Advanced Study, NASA program [HST-GO-14747, NNG16PJ25C, 17-ATP17-0034]; JSPS Overseas Research Fellowship; JSPS Research Fellowship for Young Scientists; National Science Foundation [AST-1410155]; Japan Society for the Promotion of Science, KAKENHI [17H01114]; NASA [NAS5-26555]; W. M. Keck Foundation