PA1: Fixed PLA
PA1: Speedup getMistakes
HW1: Finished
HW2: Q3-Q4
HW2: Q17-18
WH2: Fixed Q17-18

refer: https://gist.github.com/ericzhang-cn/8277581
WH2: Q19-20
Merge remote-tracking branch 'origin/MachineLearningFoundations'