Initialize page_manager.

Page manager now:
- Caches mapped pages and page_block structs
- Can unmap memory ranges
- Unmaps extra kernel memory during it's init

src/kernel/memory.h

@@ -14,6 +14,8 @@ public:
 
 private:
 	friend class page_manager;
+
+
 };
 
 extern memory_manager g_memory_manager;