Tuner for `rslocal()`

[philipp-baumann]

Hi Leo,
as mentioned some ideas for a later pull request to add a tuning wrapper to rslocal.

This is what such a tuner might tackle:

• If new sets of samples are predicted, best configuration of the three parameters is empirically evaluated. The user would therefore be able to provide combinations of those. (i.e., full-factorial or predefined combinations).

• Besides heuristic parameter optimization, such a wrapper could also provide clustering to narrow down exhaustive search of a spectral library.

• Such a tuner might also implement early stopping to make search more efficient.

Is there anything else to consider for such a functionality? I hope to soon find some time to contribute with some code to achive this.

Cheers,
Philipp