feature: Add character limit to settings.

[shanecelis]

Thank you for this crate! This was really easy to integrate and did exactly what I wanted except I needed a character limit option. My change adds a character limit setting and fires an event when the character limit inhibits character insert.

I did this work for bloomdigital.to; they support open source and wanted to contribute this work back to the community, which I'm grateful for.

[rparrett]

Thanks! Let me give this some brief thought. I had some existing vague plans for input filtering that I probably won't actually implement. But I'll likely merge as-is.