Lab2

Here are my suggested edits to lab2. After talking to the TAs and students in the class, we decided that timing things was too complicated for a beginning lab (not to mention that it isn't part of this lab's objective), so we removed those problems. The plan is to include timing in the profiling lab.
"It behave" -> "It behaves"
"faster.On" -> "faster. On"
Are we sure we want to say that np.ravel returns a view?  That is not true in all cases.
It would be more correct to say that "Ravel flattens an array." (as the documentation words it).  We sidestep telling them whether it is a view or copy.