PEP8 indentation fix
Remove double-space
Add more detailed description for score method
Improve description of base_estimator parameter
Add tests for more types of sparse matrices
Derive Ransac also from MetaEstimatorMixin
Document use cases of is_*_valid functions
Improve and document n_trials_ attribute
Fix parameter description of X and y
Change naming scheme of variables for consistency
Fix return value description of predict
Fix y paramter description of score
Change linear_model access and call explicitly with kwargs