New version of RUR-PLE (0.9.8)

After receiving some suggestions from Andy Judkis, a high school teacher who uses Rur-ple in his classes, I made the following changes to rur-ple.

• I added an "output pane" in the robot world window. Users can now put "print" statements in their programs, and the result will appear in the output pane. This should be useful in "tracing" the program flow.
• I added two new instructions that can be used in robot programs: input_int("optional text") and input_string("optional text: e.g. Enter your name.") This is an undocumented feature for now.
• I fixed an obscure "bug" discovered by Andy. When the "World file" is visible, the display was not updated when giving some beepers to the robot. This did not affect in any way the program execution; furthermore, most of the time, the world file viewer was probably hidden. Still, it should now be fixed.
• Finally, I had removed the requirement to save a program before running it. However, I had made it such that a dialog would pop up if a user was trying to quit without saving a program. Apparently, it would sometimes cause the program to hang. I could not reproduce the bug ...