Add spin.js and its jQuery plugin.
Bold font for .post .footer .date (even if it doesn't belong in this feature ;P).
A first shot at adjusting the default infinitescroll behavior to use spin.js.

 * use infinitescrolls opts.loading.start/.finish to control the content of the infinitescroll loading message – removes the need for the ugly setTimeout hack
 * #infscr-loading becomes #loading
 * move #loading message from sidebar footer to the bottom of #posts
 * prevent accidentially messed up loading order by pausing infinitescroll until newElements have been appended
 * use margin-right/-left instead of padding-right/-left on #posts to add offset for the sidebar to facilitate centering of #loading

This temporarily breaks the "custom trigger infinite scroll" option.
Remove obsolete option.
If infinite scrolling is enabled, add CSS-class .infinite-scrolling to body.
Don't show .pagination on .index pages if .infinite-scrolling is enabled; adjust .custom-trigger-infinite-scrolling .pagination appearance.
Change .post .footer color from "Darks" to "Mids" for .no-touch and :hover.
Correctly position #loading for the (default) "header-right" option.
WiP: Add the "new" Tumblr Audio Player (about one year late: http://staff.tumblr.com/post/46963344946/listen-up-our-audio-player-just-got-super-rad).
Remove fixTumblrAudio() and Co.
Tidy .audio .meta styles, bump CSS/JS sources.
Fix audio player size on permalink pages.
Localize audio download link text.
Add a spinner to #copyright, too; invoke infinite scroll a bit later.
Introduce $border-radius.
Introduce options to set "Sidebar Text Alignment" and "Avatar Style".
Bring new options "Avatar Style" und "Sidebar Text Alignment" to life via CSS, make use of the new $border-radius.
Bump CSS.
Fix infinite-scroll's position detection.
Fix infinite-scroll when starting not at the first page (e.g. "/page/2").