ParsEval labels

One sharp-eyed student has pointed out the the labels on precision and recall have been switched in the pcfg-eval() function in our skeleton code. I have updated chart.lsp to fix the bug, and you can copy the updated version to your home directory if you want. It is not required though, and should make no difference to your discussion, except that which number is labelled precision or recall in your output may differ depending on which version of the code you have.