Add support for dotted or dashed barlines

[topchyan]

Section 4.8 suggests: https://abcnotation.com/wiki/abc:standard:v2.2

A dotted bar line can be notated by preceding it with a dot, e.g. .| - this may be useful for notating editorial bar lines in music with very long measures.

Working on scores with non-trivial time-signatures transcribers often use dotted or dashed bar lines to help players navigate through them.

For example, a player may benefit by looking at this 28/8 measure and seeing that it is comprised by 3+2+2 + 3+2+2 + 3+2+2 + 3+2+2 with help of these dotted lines.

This situation is very common among the classical pieces of the Ottoman era

[paulrosen]

That sounds like a useful addition. I don't know when I will get to it but I'll try. I'd welcome a pull request.