add metatune param, now against 1.9-dev

[ahihi]

adds support for the metatune functionality recently merged into SuperDirt.

to summarize:

• WAV files can contain pitch metadata in a smpl chunk, commonly used by samplers for automatic pitch mapping
• SuperDirt now reads and stores this metadata for each loaded sample
• when the dirt_sample synth is passed metatune = 1, it tunes sample playback relative to the sample's pitch metadata

so given e.g. an instrument sample foo:2 recorded at F#4 and tagged as such in its metadata, it is now possible to do d1 $ note "c3" # s "foo:2" # metatune 1 and it will actually play at C3!

metatune defaults to 0, in which case C4 is used as the reference pitch, just like before. C4 is also the fallback when metatune = 1 but the specified sample lacks pitch metadata.

[yaxu]

thanks!