Looperchart: update for Boss DD-20

["Sjaak" <tcplugin@scarlet.be>]

For Per Boysen: I have some Boss DD-20 updates for your comparison chart of
looping devices. 

* Overdub: Yes
* Undo: No
* Multiply: No (if you mean copying a loop)
* Presets: 4 (flash RAM)
* Max number of loops: 2. Example: if preset 1 and 2 are of the same delay
type, you can record 2 loop's with different length
* Audio channels, Tracks: 2
* Stereo recording: Yes
* Built-in storage option: No

Regards,
Sjaak