fixed Texture3D and added simple gradient example
fixed Texture3D and added simple gradient example

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