New features

• Update Tensor to introduce Tensor View !32 (merged)
• add broadcasting to binary operator !30 (merged)
• update scheduler for RNN support !37 (merged)
• Add learning mechanism !48 (merged)

new operators

• Erf !20 (merged)
• Concat !20 (merged)
• Gather !20 (merged)
• ReduceMean !20 (merged)
• Reshape !20 (merged)
• Slice !20 (merged)
• Transpose !20 (merged)
• Memorize !37 (merged)
• Pop !37 (merged)
• Tanh !37 (merged)
• Sigmoid !37 (merged)
• LSTM !37 (merged)

Backprop kernel

• TODO @pineapple !48 (merged)