Week 8 adjustments from Robert

Updates Patricia's branch week8:

1. merged main
2. Adjusted file structure and renamed pages. adjusted toc a bit too (titles)
   1. most significant change here is addition of a new page (2nd section) to separate events and random variables. files are now events and variables
3. Adjusted text on front page (same commit as above).
   1. added paragraph at end to point out a few key things (and describe the journey)
   2. probably good enough as-is, but if we have spare time let's revisit it later
4. split page 2 into 2 pages. moved the continuous stuff over to page 3 and outlined more on page 2
5. outlined a case study that we can carry along the pages: discharge in two rivers. this allows connection to the other pages (last year; rest of risk-reliability book)
6. left your last 2 pages mostly as is but added a couple notes as it related to the stuff i foresee myself adding
7. added 1- and 2-random variable pages from last year as sub-pages of the last (new) section

Notes/comments:

1. I added material that i think makes the story better and supports what we will be doing on friday of 1.8; i think it is feasible but we can of course cut cut cut if i don't get my part in.
2. A section somewhere that emphasizes the concept of density would be worth the effort; students can always be reminded about density, especially in higher dimensions.
3. I think it could be useful to include some stuff from last year in week 1.8. See archived version here. makes sense to stick it at the very end if we can add an example that compares the quantitative effect of the multivariate distribution (e.g., calculate and for a few different models, such that the mean/variance of the marginas and correlation coefficient remain constant (change marginals and copula). RIsk/reliability introduction can be left out. Let's discuss.