Fix issue #96.
Read par times and calculate the score.

I haven't added par times to the XML files yet, though. Also, there's
no way for another class to know the score yet. I'll do that later.
Calculate the score.

Data related to the score is stored in a LevelScoreData structure, and
this structure is passed to any method that listens for the
Simulation's OnCompletion event. For now, everything is printed
to the console, but that should change pretty quickly. :)
Add par times.

These are untested, though, and may need to be balanced.
Make level 12 easier.

This reduces the need for the usage of user-placed platforms, but
before, reaching the goal required too much precision.
Merge branch 'master' into scoring-system
Merge pull request #100 from Jjp137/scoring-system

Scoring system (to Michael's branch)