Function fl::smush::vrule4_smush

pub fn vrule4_smush(c1: u8, c2: u8) -> Option<u8>

Rule 4: HORIZONTAL LINE SMUSHING (code value 2048)

Smushes stacked pairs of "-" and "_", replacing them with a single "=" sub-character. It does not matter which is found above the other. Note that vertical smushing rule 1 will smush IDENTICAL pairs of horizontal lines, while this rule smushes horizontal lines consisting of DIFFERENT sub-characters.