added PCA notebook to the NEWS.
Merge pull request #2165 from kislayabhi/develop

added PCA notebook to the NEWS.
memory leak fixed
Merge pull request #2166 from mazumdarparijat/decision_tree

memory leak fixed
add to news
Merge pull request #2168 from Saurabh7/develop

minor changes mkl nb
added sum and squared sum methods in CKernel