Configurable channel mapping

[brenthmiras]

Hi, I am currently looking at this library and it seems that this parses specific bms format only. I think it would be better if we can configure the channel mapping without modifying the code. A configuration file perhaps?

[dtinth]

Hi, Notes.fromBMSChart also accepts an optional options argument which allows you to specify custom channel mapping.

Let me know if you still have questions, Thanks! :)