Give themers tangible, user-friendly template functions to take full advantage of structured post formats.

* the_audio()
* the_video()
* the_image()
* get_the_media()

Also introduces:

* get_the_extra_content()
* the_extra_content()

Those two functions are like their non-extra versions, except that they
will have any post-format bits extracted. e.g. It's an image post, for
which the_image() will extract an <img /> tag. the_extra_content() will
output the content *without* that image.

props wonderboymusic. Herculean effort. fixes #23572

git-svn-id: http://core.svn.wordpress.org/trunk@23819 1a063a9b-81f0-0310-95a4-ce76da25c4cd