Fix string encoding

[jeparlefrancais]

Closes #224

Correctly encode characters that takes more than 1 byte.

• add entry to the changelog

[github-actions]

Coverage after merging fix-string-encoding into main will be

86.09%

Coverage Report for Changed Files

File	Stmts	Branches	Funcs	Lines	Uncovered Lines
src/generator
utils.rs	94.14%	100%	96.88%	93.82%	135, 29–31, 321, 33, 335–336, 35, 352–355, 59, 69, 79, 89