Reorganize output/ directory

Currently, information about *how to this midi file was generated* are poorly stored in their name. For instance:

notesR_generated_by_double_independances.mid

Which gives the input notes and the generation method, but not the clustering method or the markov chain order.

A way to go is to create a hierarchy of directory, ending with something like : `output///.mid`. This is not really useful.

Then, another solution is to encode the data in a well known format named RDF:

[rdfs:label "myfavorite.mid"; mg:generationMethod "DI"; mg:abitraryProperty 42].

Which is readable as a file named *myfavorite.mid* generated using DI generation method and 42 as an arbitrary property.

The file hosting all the lines could be named *metadata.ttl*.