use oembed for vimeo and soundcloud.

youtube doesn't allow cross-origin requests, so we have to use the
old method for now.

js/babl/public/index.html

@@ -37,6 +37,26 @@
				}
			}
			function oembedElement(url, oembedEndpoint) {
				var el = document.createElement('a');
				el.href = url;
				el.textContent = url;
				var xhr = new XMLHttpRequest();
				xhr.open('GET', oembedEndpoint + '?format=json&maxwidth=450&url=' + url);
				xhr.onreadystatechange = function() {
					if (xhr.readyState == XMLHttpRequest.DONE) {
						console.log(url, xhr.status);
						var tmpEl = document.createElement('div');
						tmpEl.innerHTML = JSON.parse(xhr.responseText).html;
						el.parentElement.replaceChild(tmpEl.firstChild, el);
					}
				};
				xhr.send();
				return el;
			}
			var word_matchers = [{
				re: /https?:\/\/.*youtube.com\/watch\?v=([a-zA-Z0-9-]+).*/,
				fn: function(match) {
@@ -49,38 +69,10 @@
				}
			}, {
				re: /https?:\/\/.*soundcloud.com\/.*/,
				fn: function(match, msgEl) {
					var el = document.createElement('a');
					el.href = match[0];
					el.textContent = match[0];
					var xhr = new XMLHttpRequest();
					xhr.open('GET', 'https://soundcloud.com/oembed?format=json&maxwidth=450&maxheight=315&url=' + match[0]);
					xhr.onreadystatechange = function() {
						if (xhr.readyState == XMLHttpRequest.DONE && xhr.status == 200) {
							var data = JSON.parse(xhr.responseText);
							var tmpEl = document.createElement("div");
							tmpEl.innerHTML = data.html;
							msgEl.replaceChild(tmpEl.firstChild, el);
						}
					}
					xhr.send();
					return el;
				}
				fn: function(match) { return oembedElement(match[0], "https://soundcloud.com/oembed"); }
			}, {
				re: /https?:\/\/vimeo.com\/([0-9]+).*/,
				fn: function(match) {
					var el = document.createElement("iframe");
					el.src = "//player.vimeo.com/video/" + match[1];
					el.sandbox = "allow-same-origin allow-scripts allow-popups";
					el.width = 420;
					el.height = 315;
					el.setAttribute("frameborder", 0);
					return el;
				}
				fn: function(match) { return oembedElement(match[0], "http://vimeo.com/api/oembed.json"); }
			}, {
				re: /https?:\/\/.*(png|gif|jpg|jpeg)$/i,
				fn: function(match) {