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This branch contains vastly improoved kernel memory
subsystem with following new features:
    * 2M/1G pages
    * Lazy copying/lazy memory allocation
        * Used for speeding up ASAN memory allocation
        * Kernel memory is also lazily allocated
    * NX flag
    * Buddy physical memory allocator
    * O((log N)^2) region manipulation
    * More convinient syscall API
    * IPC with memory regions of size larger than 4K
        * Not used at the moment but would be useful
          for file server optimization
    * Reduced memory consumption by a lot
    * All supported sanitizers can work simultaniously
      with any amount of memory (as long as bootloader can allocate enough memory for the kernel)

The code is mostly located in kern/pmap.c
A set of trees is used for holding metadata (nodes are of type struct Page):
    * A tree describing physical memory
    * One tree for every address space (for every environment and kernel)

TODO
    * Replace user_mem_assert with exception-based code
        * copyin/copyout functions
    * Refactor address spcae and move all kernel-only memory
      regions to cannonical upper part of adress space
      (this requeres copyin/copyout functions because
       ASAN should never touch userspace memory)