MOD modify tree pattern kernel, remove tottering.
MOD save output in function model_selection_precpmputed.

* MOD the way to calculate WL subtree kernel, correct its results. - linlin
* ADD *kernel_train_test* and *split_train_test* to wrap training and testing process. - linlin
* MOD readme.md file, add detailed results of each kernel. - linlin

* MOD floydTransformation function, calculate shortest paths taking into consideration user-defined edge weight. - linlin
* MOD implementation of nodes and edges attributes genericity for all kernels. - linlin
* ADD detailed results file results.md. - linlin
* MOD Weisfeiler-Lehman subtree kernel and the test code. - linlin

* ADD delta kernel. - linlin
* MOD reconstruction the code of marginalized kernel. - linlin