Larger sprites and scrolling

This is a rather technical update in which the sprites are now 36x36 (instead of 24x24). To not restrict the size of the world, the world can now be larger than the screen. The player will always be displayed at the center.

A line of sight algorithm has been added to decide what tiles are visible at any moment. A maximum viewing distance (a circle) has also been set because otherwise it could happen that part of the room you are 'viewing' falls outside of the screen.

However, I have also made changes to the combat system: Melee attack hit chance is now 100% and the dex (dexterity) stat has been removed. Ranged attacks (such as throwing) also start out with a 100% hit chance but for each tile traveled 5% is subtracted. The blk (block) stat that is on shields, and that represents the chance of completely blocking an attack, is now a percentage. I made these changes to make it simpler to reason about what will happen in a particular situation.