FTR: Map: Stairs

[proof88]

Using '/' and '' map elemens to represent stairs.
A single such character will generate stairs having height of 1/3 or 1/4 of the height of a regular 1x1x1 map element (block).

The following improvements are also required to be done:

• fast collision check because this feature might significantly increase the number of map elements to be checked against collision: CR/OPT: Fast Player Collision Check #150;
• player physics change: player shall be pushed upwards upon side-colliding with any map element where the difference between the top edge Y coordinate of the map element and the bottom edge Y coordinate of the player object is less than a predefined threshold. This way players dont need to jump onto the stairs, will be automatically aligned on the stairs where applicable: FTR: Physics: Player Vertical Auto-Alignment upon Horizontal Collision #343.