Update readings

[CWWhitney]

There are good scientific papers and chapters on DA that explain things succinctly.

• Hubbard (Swap for Keeney or Howard Abbas)

Look again through the readings and determine which should go

[CWWhitney]

Related to #21

[CWWhitney]

Specifically, make the Solutions paper reading 1.
Drop Hubbard

[CWWhitney]

Reed at al (2009) from lecture 5 is not in the citations (add later)