MATH 239: trivial single-word/formatting changes.
Merge branch 'master' of github.com:christhomson/lecture-notes

Conflicts:
	math239.pdf
MATH 239: no longer claiming example 7.19 is not a Hamiltonian cycle.
MATH 239: spelling of colo(u)r is now more Canadian.
MATH 239: added maximum/maximal matching definitions.
MATH 239: a few more minor rewordings.