Refactor Gtable from Struct to Type Alias

[DylanMeeus]

Gtable is just a lightweight wrapper around []float64 at the moment.
This can be refactored into a type Gtable []float64 alias. Or, even better perhaps, type Table []float64 to represent any kind of table (guard table / wave table).

[JavascriptMick]

interested in contributing, not sure if this is still a good issue to start with? seems a bit pointless

[DylanMeeus]

Hi,

This is more a "quality of life" improvement. Mainly to help the type system clarify exactly what our types represent. It's indeed pretty low-hanging fruit and does not have the largest impact. If there's another issue you are interested in, I can help you get started on those as well. :-)