Added record stats

The stats page now also shows an application's recorders and for live applications also their records.

The `rtmp_stat` directive has a new option `record` to toggle the display of record information.

Some screenshots:
Recorders: http://i.imgur.com/sZnKKO4.png
Records: http://i.imgur.com/PPW8zYN.png

To access the filename of a currently running record, i had to get access to the static ngx_rtmp_record_make_path function, so i added another publically visible one called ngx_rtmp_record_get_path.
If for some reason, the filename request needs to be denied, it can be added there ( i don't see a reason for that right now tho ). Hope that's fine, arut.