Intro nb added
clean up and regression
preprocessor example
Regression nb
lars section
some more additions
revamp structure
refine lars and intro
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
extend svm nb
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
some cleanups
update the MatrixOperations class