Factor out build_features function
Factor out build_features function

1. in order to better re-use code in leave one out and permutation test

thekingofkings/chicago-crime,thekingofkings/chicago-crime,thekingofkings/chicago-crime,thekingofkings/urban-flow-analysis,thekingofkings/chicago-crime,thekingofkings/urban-flow-analysis,thekingofkings/urban-flow-analysis,thekingofkings/chicago-crime,thekingofkings/chicago-crime,thekingofkings/urban-flow-analysis,thekingofkings/urban-flow-analysis