rename pos->center in constructor of ellipse
rename pos->center in constructor of ellipse

Eric89GXL/vispy,QuLogic/vispy,julienr/vispy,drufat/vispy,kkuunnddaannkk/vispy,inclement/vispy,julienr/vispy,sh4wn/vispy,QuLogic/vispy,michaelaye/vispy,sh4wn/vispy,RebeccaWPerry/vispy,ghisvail/vispy,ghisvail/vispy,inclement/vispy,jdreaver/vispy,michaelaye/vispy,QuLogic/vispy,bollu/vispy,dchilds7/Deysha-Star-Formation,jay3sh/vispy,bollu/vispy,sh4wn/vispy,ghisvail/vispy,michaelaye/vispy,bollu/vispy,jay3sh/vispy,julienr/vispy,jay3sh/vispy,sbtlaarzc/vispy,drufat/vispy,inclement/vispy,jdreaver/vispy,Eric89GXL/vispy,srinathv/vispy,RebeccaWPerry/vispy,sbtlaarzc/vispy,dchilds7/Deysha-Star-Formation,RebeccaWPerry/vispy,kkuunnddaannkk/vispy,dchilds7/Deysha-Star-Formation,srinathv/vispy,drufat/vispy,kkuunnddaannkk/vispy,srinathv/vispy,sbtlaarzc/vispy,Eric89GXL/vispy,jdreaver/vispy