- Implemented audio support with Video.js.

What changed:
Added uploaded/direct audio playback paths in 
[index.php](/Users/tyemeclifford/Documents/GH/mediaplayer/index.php) and 
[embed.php](/Users/tyemeclifford/Documents/GH/mediaplayer/embed.php).
Added common audio upload support: MP3, M4A, AAC, WAV, FLAC, OGG, OGA, 
OPUS.
Added waveform poster generation for uploaded audio via ffmpeg, stored 
like normal thumbnails under media/thumbs/.
Updated add/edit forms to accept media files, not just video files.
Added audio-friendly labels like Audio, 320kbps, 256kbps, 128kbps.
Updated docs and changelog.

admin/youtube_import.php

@@ -600,7 +600,7 @@ render_head('YouTube Importer — Admin', '
     <aside class="admin-nav">
       <div class="admin-nav-label">Navigation</div>
       <a href="index.php">Videos</a>
-      <a href="add.php">Add Video</a>
+      <a href="add.php">Add Media</a>
       <a href="youtube_import.php" class="active">YouTube Importer</a>
       <hr class="nav-divider">
       <a href="settings.php">Settings</a>