The plotting with axis labels in multiples of pi is something new to Maple 11 and can be done fairly easily.  For example the tips and techniques that Maplesoft put out last April (can be found here) has a section on how this can be set.  As for drawing polygons with the angles labeled, to my knowledge there is no automatic way to do this.  One way is to combine the polygon plot with a Text plot with the angle values and the location to start the text.  The second option is to draw in the text after the polygon is plotted by using the plot annotation (also discussed in the above tips document).

Scott