* Fix loading old logit model.
* Add a helper script for converting old pickle file.
* Add version as a model parameter.
* Remove the size check in R test to relax the size constraint.
* Add missing R doc for passing linting. Run devtools.
* Cleanup old model IO logic.
* Test compatibility on CI.
* Make the argument as required.
Squashed commits:
[9109887] Added test for eta decay(+1 squashed commit)
Squashed commits:
[1336bd4] Added tests for eta decay (+2 squashed commit)
Squashed commits:
[91aac2d] Added tests for eta decay (+1 squashed commit)
Squashed commits:
[3ff48e7] Added test for eta decay
[6bb1eed] Rewrote Rd files
[bf0dec4] Added learning_rates for diff eta in each boosting round