Accept arrays in feature functions

[tsalo]

Summary

To reduce the number of temporary files we may need to write, we should allow the feature functions to accept arrays in addition to files.

Additional Detail

Next Steps

1. Check datatypes of inputs to feature functions. If str, load the file. If array, use that directly.
2. Update the docstrings.
3. Add tests for both types of inputs.

[vinferrer]

Should we wait for complete python implementation? is because i am seeing the inputs and most of the time is something generated by melodic

[eurunuela]

Indeed, we cannot work on this issue until we drop MELODIC.