for merge
Merge branch 'master' of https://github.com/Data2Semantics/d2s-tools.git
Merge branch 'master' of https://github.com/Data2Semantics/d2s-tools.git
Merge branch 'master' of https://github.com/Data2Semantics/d2s-tools.git
Merge branch 'master' of https://github.com/Data2Semantics/d2s-tools.git
normalize SparseVector bugfix, division by 0