Need algorithm for how composition events are fired

[garykac]

We need a algorithmic description of how composition events are fired.

compositionstart, compositionupdate, compositionend

See https://w3c.github.io/uievents/#events-composition-order

[garykac]

For readability and manageability, this would ideally be separate from the basic key event algorithm (#142), but we'll need to have appropriate hooks for that.

[garykac]

Handling this as part of specifying the keyboard/input/composition events. See #142