Chapter on fields from CRing project

This is to test if it is feasable to have a chapter on fields which
comes before the chapter on commutative algebra. The idea being that
people with an undergraduate algebra course should be able to read it.

The text of the chapter is take from the CRing project with permission
from Akhil Mathew. Contributions to this chapter in particular from:
Akhil Mathew, Geoffrey Lee, and Ryan Reich
Mostly coding style issues in fields chapter
Coding style issues and a bit of new material
Rewrote parts of the chapter on fields
First version of section on Galois theory
First draft of the fields chapter is done
Fix references to point to the results moved to fields.tex
Merge branch 'develop'

Time to merge in the development on the chapter on fields.

Thanks to the people of the CRing project for writing the
initial version of this chapter. These people are
Shishir Agrawal, Eva Belmont, Zev Chonoles, Rankeya Datta
Anton Geraschenko, Sherry Gong, Francois Greer, Darij Grinberg
Aise Johan de Jong, Adeel Ahmad Khan, Holden Lee, Geoffrey Lee
Akhil Mathew, Ryan Reich, William Wright, and Moor Xu
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