MATH 239: added April 5, 2013 lecture.
Merge pull request #20 from jasonchutko/master

Fixed #18.
Merge branch 'master' of github.com:christhomson/lecture-notes

Conflicts:
	math239.pdf
MATH 239: reorganized graph theory section. (Fixes #13)
CS 241: added April 8, 2013 lecture.
MATH 239: added April 8, 2013 lecture.
CS 241: added 245 to related courses.
MATH 239: added some defns that weren't formally defined(?).
MATH 239: reorganized some defns, added girth definition.
MATH 239: Various fixes in spelling, references, and images.