fix some typos in a2 writeup and make lines 80 chars
fix some typos in a2 writeup and make lines 80 chars

compsci697l/compsci697l.github.io,kchen92/cs231n.github.io,kchen92/cs231n.github.io,cs231n/cs231n.github.io,jt120/jt120.github.io,dolittle007/cs231n,jt120/jt120.github.io,cs231n/cs231n.github.io,compsci697l/compsci697l.github.io,dolittle007/cs231n,cs231n/cs231n.github.io