Huffman file format

   First 4 bytes contain file size of uncompressed file (little endian).

   Bits following describes the huffman tree:

      0 -> this is an internal node, next bit describes the left branch
      1 -> this is a leaf node, next 8 bits describe the byte value

      Size of tree is at most 9*256 + 255 bits (256 leaf nodes, 255
      internal nodes).

   Following bits are the huffman data, 0 for following left branch, 1
   for following the right branch.  0 bits are padded at the end to
   align to byte boundary.

   In the case where there is only one leaf node, the huffman data
   will be missing, since the file can be constructed using the tree
   data and file size alone.

Encoding the huffman tree

   1. Build huffman tree using conventional methods
   2. Dump tree using preorder traversal

Decoding the huffman tree

   create root node pointer, push onto stack
   L1: read next bit from file
      if 0 read:
         create node, set pointer on stack to point at node, push onto stack
      if 1 read:
         create leaf node using next 8 bits
         set pointer on stack to point at node
	 L2: if stack contains only this leaf, process is complete.
         pop stack
         if right pointer on stack is empty
            set pointer to right pointer on stack
         else
            pop stack, goto L2
      goto L1