The Windows release.

• Core:
  • Make it work on windows, thanks to appveyor.
  • Make sure that the save directory is created before using it.
  • Add the student code to the GitHub automatic bug reports.
• UI:
  • Make it possible to open the mission text in an external windows.
• Buggles:
  • Display the buggles' errors in the verbose world diff.
  • Translate these messages even in the Python bindings.
• Pedagogical content:
  • Hide the functions in welcome/variables.java: That's too early.
  • In 'stairway to heaven', we are using a global variable to count the amount of steps done so far. Rename it inTeerNal_Steep_Count to ensure that it will never clash with any variable created by the learner.