generate towers and cities.

cities aren't very exciting yet. and they don't perform well.

js/pixl/public/trixl.html

			});
		}
		var rand = function(lo, hi) {
			var both = hi !== undefined,
			    l = both ? lo : 0,
			    h = both ? hi : lo;
			return l + Math.round(Math.random() * (h - l));
		}
		var rgbFromCss = function(color) {
			var el = document.createElement('div');
			el.style.color = color;
			trixl.generate.many(1000, -100, 100);
		}
		trixl.generate.tower = function(pos, width, height, color) {
			range(height).map(function() {
				trixl.world.set([
					rand(pos[0], pos[0] + width),
					rand(pos[1], pos[1] + height),
					rand(pos[2], pos[2] + width)
				], {color: color || [Math.random(), Math.random(), Math.random(), 1]});
			});
		}
		trixl.generate.city = function(n, width, height) {
			range(n).map(function() {
				var pos = [rand(width), 0, rand(width)];
				var w = rand(5, 20);
				var h = rand(height);
				trixl.generate.tower(pos, w, h);
			});
		}
		trixl.geometry = {};
		trixl.geometry.circle = function(pos, radius, color) {