Function character_swaps 

pub fn character_swaps(written: &str, direction: Direction) -> String

The swaps between the two notations: music21’s characterSwaps.

A half-diminished chord is % in the lab’s tables and ø in music21’s figures, and the lab says a seventh’s quality where music21 does not.

use music21_rs::romantext::tsv::{Direction, character_swaps};

assert_eq!(character_swaps("ii%", Direction::IntoMusic21), "ii\u{f8}");
assert_eq!(character_swaps("ii\u{f8}", Direction::IntoDcml), "ii%");
assert_eq!(character_swaps("VM7", Direction::IntoMusic21), "V7");