message: README: fix links in README
  closes
diff: @@ -47,11 +47,21 @@ DEFINITIONS
  system, 4Kb on most architectures. Memory given to the allocator by
  the operating system is always in multiples of the page size, and
  aligned to the page size.
  -- **Span**: The size of memory managed by Mesh -- [currently 128
  - Kb](src/include/miniheap.h#L36).
  - It is larger than the page size to amortize the cost of heap
  - metadata.
  -- [**MiniHeap**](src/include/miniheap.h): A bitmap, metadata and associated Span for a
  - particular size of objects (size class).
  -- [**MeshingHeap**](src/include/meshingheap.h): A collection of miniheaps for a particular size
  - class, including a _current_ MiniHeap that we are allocating out of.
  +- **Span**: A contiguous run of 1 or more pages. It is often larger
  + than the page size to account for large allocations and amortize the
  + cost of heap metadata.
  +- **Arena**: A contiguous range of virtual address space we allocate
  + out of. All allocations returned by
  + [`malloc(3)`](http://man7.org/linux/man-pages/man3/malloc.3.html)
  + reside within the arena.
  +- [**GlobalHeap**](src/global_heap.h): The global heap carves out the
  + Arena into Spans and performs meshing.
  +- [**MiniHeap**](src/mini_heap.h): Metadata for a Span -- at any time
  + a live Span has a single MiniHeap owner. For small objects,
  + MiniHeaps have a bitmap to track whether an allocation is live or
  + freed.
  +- [**ThreadLocalHeap**](src/thread_local_heap.h): A collections of
  + MiniHeaps and a ShuffleVector so that most allocations and
  + `free(3)`s can be fast and lock-free.
  +- [**ShuffleVector**](src/shuffle_vector.h): A novel data structure
  + that enables randomized allocation with bump-pointer-like speed.
  