Provide hooks that signal player status

[BillyWM]

Communicate to outside world through either callbacks or events (callbacks probably preferable so that the player isn't tied to a browser environment. May like to support using this headless on Node)

A UI wants to know:

• Current row playing
• Samples(s) playing and positions within those samples

The containing page should be able to subscribe to changes in these properties.

[BillyWM]

Needs pattern-to-text method for display as data is still stored as object with raw numeric properties direct from file.