PRNG + LCG chapters

[leios]

This is a draft PR for the next set of chapters. It will include the following:

• An intro to RNG
  • a discussion of where RNG is used in different fields
  • quick histogram check to see how random your RNG is
• Diehard tests
  • Birthday spacings
  • Overlapping permutations
  • Ranks of matrices
  • Monkey tests
  • Count the 1s
  • Parking lot test
  • Minimum distance test
  • Random spheres test
  • The squeeze test
  • Overlapping sums test
  • Runs test
  • The craps test
• Linear Congruential Generators
  • Explain why they might be used in CG applications / GPU kernels (due to other RNG methods being cumbersome)

Might be biting off a bit too much, but I've been wanting to do diehard tests forever now and it'll be fun creating the testsuite.

[Amaras]

Idea: add Linear-Feedback Shift Registers as a (cheap) hardware PRNG, although it can be quite weak as a PRNG