Donchian Channels top/bottom

Donchian Channels with addition of highest low and lowest high per length. Thus creating a top and bottom channel. Cheers.

Release Notes:

Donchian Channels with addition of highest low and lowest high per length. Thus creating a top and bottom channel. Cheers

Update: Added variable input length.

Release Notes:

Adding T-variable prevents plots from crossing. Just a bit neater.
(I've always used T (stands for trigger) as quick reference for movement)