change fanchor to 0

[daslyfe]

• kinda breaking change: will change patterns without the fanchor set using fenv to be a bit brighter
• It's time to make this change, it is a source of confusion when giving workshops why the filter env behaves in a bipolar fashion by default. Imagine strumming an instrument harder, and the harmonics fading faster. Bipolar envelopes can also cause clicks if the cutoff dips too low.