Parameter name equivalency with LightGBM -- snake_case vs camelCase

The parameters for mmlspark are written in camelCase whereas the LightGBM parameters are written in snake_case. See: https://lightgbm.readthedocs.io/en/latest/Parameters.html
In addition, the parameter aliases mentioned on that page are not supported.

This adds an annoying step to migrating a project from using LightGBM to mmlspark. I understand the motivation to be consistent with typical Scala/Java conventions but it's not worth it here.

Fixing this would help adoption of this project a lot, moving the mmlspark API one step closer to being a drop-in replacement for the non-spark LightGBM API.