Improvement for memory management

[MinusPL]

Currently MicrOS maps whole 4 MB of page directory for given process when there is more memory required, that means we're wasting alot of memory for slightly faster and maybe a little bit simpler mechanism of memory mapping and pagination. To get memory back we should consider refactoring that part of OS to properly map 4 KB pages, which will allow launching OS properly on low memory systems (like 486 with 32 MB of ram).