Tangent works now; hardcoded the derivative of cosine on line 155 in
Grapher.java. This needs to be replaced with a proper differentiation
method. I disabled the turning because neither turning method (pivot
around center, pivit around circle point) was very effective. They are
commented out in the beginning of plot2d.java. Made xCircPos from plot2d
public so that Grapher could access it for differentiation. Added
printing of current angle of orientation on line 89 of plot2d