* lily/include/object-key-undumper.hh (Module): new file.

* lily/include/object-key-undumper.hh (Module): new file.

* lily/object-key-undumper.cc (Module): New file. Deserialize
keys. SCM bindings

* lily/object-key-dumper.cc (Object_key_dumper): idem.
Provide SCM bindings.

* lily/include/object-key-dumper.hh (class Object_key_dumper):
new file. Serialize object keys.

* lily/object-key.cc (dump): new function.
(as_scheme): new virtual function
(undump): new function
(undumpers): new table.

* lily/include/global-context.hh (Context): take \score key upon init.

* lily/object-key-dumper.cc (serialize_key): new file.

* lily/include/object-key-dumper.hh (class Object_key_dumper): new file.

* lily/lily-lexer.cc: remove \quote.

* lily/lookup.cc (triangle): rewrite, obviating symmetric_x_triangle().

* lily/context.cc (Context): take key argument in ctor.
(create_context): new function

* lily/lilypond-key.cc (do_compare): new file.

* lily/object-key.cc (Object_key): new file.

* lily/include/object-key.hh (class Object_key): new file.

* lily/include/lilypond-key.hh (class Lilypond_context_key): new file.