Merge pull request #147 from jiangyi15/mlp #645

Job	Run time
conda install latest tensorflow (ubuntu-20.04)	4m 5s
Build documentation	2m 36s
Unit tests (ubuntu-20.04, 3.7)	16m 9s
conda install (ubuntu-20.04)	2m 40s
Unit tests (macos-11, 3.7)	35m 10s
Style checks	2m 10s
Test uproot3 (ubuntu-20.04, 3.7)	16m 6s
Unit tests (ubuntu-20.04, 3.6)	14m 24s
Unit tests (ubuntu-20.04, 3.8)	14m 59s
Coverage (ubuntu-20.04, 3.7)	41s
	1h 49m 0s

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