Amazing changes

The library now returns an object from change, changeAt, changes and change' that reflects the changed audio unit. Previously, these functions had returned Unit (akin to set in many libraries), whereas now they return an updated value (akin to modify).

Furthermore, we've added an asGetter function to transform any graph into a getter. On change, this will get the previous values instead of modifying them.

Lastly, this version adds a get family of functions, get, getAt, gets and get' that work exactly like their analogue from the change family of functions but act as getters by using asGetter internally. Importantly, the get family of functions does not increment the change bit. An example of get is in the project's unit tests.