Move to less, improved style, fixed bugs

* Redirection wasn't being encoded properly
* CSS to LESS transition
* Improved Makefile
* Explained red color in index
* Unified link and button styles

res/song.html

@@ -1,9 +1,9 @@
 <div class="song">
     <script async src="../transpose.js"></script>
     <script async src="../sizes.js"></script>
-    <h2>%s</h2>
-    %s
-    %s
+    <h2>{name}</h2>
+    {author}
+    {origin}
     <h3>Ajustes</h3>
     <div>
 		<label>Cambiar tamaño de letra </label>
@@ -34,15 +34,15 @@
         <button class="small" onclick="transposeAdd(2)">+2</button>
         <button onclick="transpose(0)">Reset</button>
     </div>
-    %s
+    {capo_settings}
     <h3>Canción</h3>
     <div id="wholeSongDiv">
-        %s
+        {song_html}
     </div>
     <div>
-        %s
-        %s
+        {audios_header}
+        {audios_html}
     </div>
-    <a href="https://gitlab.com/parroquia-san-leandro/cancionero-25/blob/master/%s">Ver archivo original</a>
-    <button onclick="window.location = window.location.toString().slice(0, window.location.toString().lastIndexOf('/')) + '/../'">Atrás</button>
+    <a href="https://gitlab.com/parroquia-san-leandro/cancionero-25/blob/master/{latex_file}"><span>Ver archivo original (LaTeX)</span></a>
+    <a href="../"><span>Atrás</span></a>
 </div>