support removing trixls.

js/pixl/public/trixl.html

@@ -150,6 +150,17 @@
			[[+0.0, +3.0, 2], {color: [0.5, 0.5, 0.5, 1]}]
		]);
		trixl.world.remove = function(pos) {
			var key = null;
			for(var k of trixl.world.keys()) {
				if (k[0] === pos[0] && k[1] === pos[1] && k[2] === pos[2]) {
					key = k;
					break;
				}
			}
			return trixl.world.delete(key);
		}
		var angle = {x: 0, y: 0, z: 0};
		var offset = {x: 0, y: 0, z: 0};
		program.transform = gl.getUniformLocation(program, 'transform');