Started adding XML comments. This will be a long journey.

For Issue #18

I'm starting the long road to filling out the methods with proper XML documentation. Take a look at what's done so far (it isn't much) and let me know if you think the style is too verbose or not. I'm basically just copy-pasting from the official libsdl.org wiki.

Some remarks sections on the wiki are far too long to put into the remarks of the methods, so you'll notice that not all methods have full documentation.

Let me know what you think.