feature request: splitter.countDisplay helper functions

[mknj]

Some characters are double width.
It would really be nice to have a helper function for that.
This function would be very useful to generate tables for shell/cli use.

example

const a="基于gulp和browserify的项目构建工具"
splitter.countDisplay(a) // should return 34 instead of 24

It would also be nice to support the zero-width joiner.

related work: https://github.com/unicode-rs/unicode-width