Doc: improve 2.10 World music

Doc: improve 2.10 World music

* Move Turkish note names table in the relevant subsection;
* Rename "non-Western notation and tuning systems"
    into "Common non-Western notation"
* Add subsection for tuning systems
* Add non-Western section in Glossary.
* Add glossary entries (with stubs)
* Add @seealso whereever possible
* Improve wording, consistency.