Check variance of CV-Estimators against the logic presented in the lecture

[olivierlabayle]

• [x] Check with lecture 5 or 4 and document.

• [x] Fix bug in cv predictions

• [x] One Step

  • [x] Check code
  • [x] Update to weighted estimate by fold
  • [x] Is the IC correct ?
  • [x] Is the variance correct ?
  • [x] Write documentation

• [x] TMLE

  • [x] Check code
  • [x] Update to weighted fluctuation by fold
  • [x] Is the IC correct ?
  • [x] Is the variance correct ?
  • [x] Write documentation

• [x] Caching

  • [x] Check code
  • [x] Document

• [x] Review