Time series

Changelog:

- fixed a typo in the index j k on slide 9 and added more explicit details to the calculation

- slide 19 said $\gamma^{(1,2)}_\tau$ when it should have said $\gamma^{Y}_\tau$

- the example on page 30 said $z^1$ not $z^2$

- the notation for the variance of the white noise on page 34 was an old convention, this has been updated