Create a virtual memory manager (VMM)

[4e554c4c]

Overview

So we already have a pretty great, basic physical memory manager, but we'll need much more flexibility to continue with scheduling and getting a user space. For this reason I'm opening this issue as a tracking issue for the virtual memory manager, and I'll update it as different features are implemented. We already have some basic features implemented (stack allocation from BlogOS, for example) but these are quite limited (no deallocation, constant size, no growing stacks, etc).

Features

• Basic VMM features
  • Stack Allocation
    • Allocation
    • Deallocation
    • Automatic stack growth
  • Separate userspace/kernelspace virtual memory
    • Higher-half kernel -- mostly
    • Separate userspace memory per-process
  • Reference counting and COW