cross-validation enabled for TreeMachine, added CART notebook
Modular API for RF and minor fixes
data submodule updated
Added support for softmax visible units and sampling with evidence to CRBM
Merge pull request #2315 from khalednasr/rbms

Added support for softmax visible units and sampling with evidence to CRBM
loss functions added for Gradient Boosting
Minor refactoring in:
    * all the StructuredModels
    * all the StructedOutputMachines
to provide support for sparse joint feature vector
Modified all the StructuredOutputModels to include
get_sparse_joint_feature_vector() method.
Implemented CHashedMultilabelModel class to faciliate feature hashing in
multilabel scenario.
Added unit-test for CHashedMultilabelModel
update the MatrixOperations class
update the base class
update the first KL method
update the second KL method
update the third KL method
Merge pull request #2310 from mazumdarparijat/documentation

cross-validation enabled for TreeMachine, added CART notebook
add_to_dense() method added in SGSparseVector for adding a dense vector
Merge pull request #2312 from yorkerlin/develop

update  all KL methods
Minor refactorings and changes in:
    * all the StructuredOutputModels
    * all the StructuredOuputMachines
to remove redundant methods and intializations
fix abstract of log-det notebook