- Code reviewed by Olivier B., thanks!
- Lots of comments added
- Unused code removed
- Looping in Elemwise is now done so the contiguous dimension of the output is
  looped over in the inner-most loop. It does not change anything in the
  non-inplace case (the output was C-contiguous), but can lead to really
  better performances (at least 7x) in the inplace case.