[body] significant changes

* fixed sign error in graphs-are-matroids proof
* fixed sentance structure, typos, grammar
* added section on generalized greedy algorithms
* added comments on specifics of wording in certain paragraphs
* improved section on kruskals algorithm
* improved section on GGA, improved that paragraph
* added a bad proof of GGA-solves-matroids
* added example of kruskals algorithm
* added page numbers to references of clrs
* fixed typos
* added example of cycle matroid