Merge branch 'release/v0.0.0'
Merge https://github.com/svs14/GradientBoost.jl into develop
Renamed gb_learner.jl to gb_bl.jl and respective tests. Renamed module GBLearner to GBBaseLearner.
Rename class GBL to GBBL.
Rename of GBProblem to GBLearner. Rename gbp to gbl. Updated README.md.
Merge branch 'feature/api-refactor' into develop