Add operators for combining oscillators together

[sofian]

Since by default the oscillators are set in the [0, 1] range the usual operations of addition will not work as planned. So we should provide a way to easily add oscillators.

Notice though that an average of oscillators would do the trick; furthermore it will ensure result stays within [0, 1] so perhaps that's all we would need. Something to think about...

More broadly we can think about ways to combine multiple sources together (composition?)

• add
• subtract
• min
• max
• average
• not
• and
• or
• xor