add missing exports (#4) (Playback, Plugins, PsEnums)

fix #4
see #4, and Discord (for Plugins export)

src/Common/Enums/index.ts

@@ -4,3 +4,4 @@ export * from "./FontStyles";
 export * from "./Fonts";
 export * from "./TextAlignment";
 export * from "./TieTypes";
+export * from "./PsEnums";

src/Plugins/index.ts

@@ -0,0 +1 @@
+export * from "./Transpose";

src/index.ts

@@ -3,3 +3,5 @@ export * from "./MusicalScore";
 export * from "./Util";
 export * from "./Common";
 export * from "./Display";
+export * from "./Playback";
+export * from "./Plugins";