export InstrumentNames class (#111)

adding the new class to exports so that they can be used from the build

src/MusicalScore/index.ts

@@ -2,6 +2,7 @@
 
 export * from "./Exceptions";
 export * from "./Instrument";
+export * from "./InstrumentNames";
 export * from "./InstrumentalGroup";
 export * from "./Label";
 export * from "./MusicSheet";