move everything to subfolder theories/

theories/prelude/lexico.v

theories/prelude/list.v

theories/prelude/listset.v

theories/prelude/listset_nodup.v

theories/prelude/mapset.v

theories/prelude/natmap.v

theories/prelude/nmap.v

theories/prelude/numbers.v

theories/prelude/option.v

theories/prelude/orders.v

theories/prelude/pmap.v

theories/prelude/prelude.v

theories/prelude/pretty.v

theories/prelude/proof_irrel.v

theories/prelude/relations.v

theories/prelude/set.v

theories/prelude/sorting.v

theories/prelude/streams.v

theories/prelude/stringmap.v

theories/prelude/strings.v