breaking: Rename events to use _ instead of :

[PuruVJ]

Currently we use neodrag:start, neodrag:end and neodrag events. The colon(:) causes issues with Svelte Language tools, and maybe in other environments as well.

From v3, rename these to neodrag_start, neodrag_end.

Why not camelcase(neodragStart)? Because most people who'll be listening to these events are the svelte folks(onneodrag_start), where events are now lowercase, hence we need _ to keep it readable, or the plain js users, who will have the same issue