Added support for monoplex string atoms and used it for LilyPond header variables options TER
Added support for monoplex string atoms and used it for LilyPond header variables options TER

grame-cncm/libmusicxml,arshiacont/libmusicxml,arshiacont/libmusicxml,arshiacont/libmusicxml,grame-cncm/libmusicxml,arshiacont/libmusicxml,grame-cncm/libmusicxml,dfober/libmusicxml,dfober/libmusicxml,grame-cncm/libmusicxml,grame-cncm/libmusicxml,arshiacont/libmusicxml,grame-cncm/libmusicxml,dfober/libmusicxml,dfober/libmusicxml