Should do:
- Use stdint.h and inttypes.h to standardize the int sizes and format strings.

- Add --DU option to fully report disk usage, taking into account files that
  are not displayed in the output.

- Should be a better way code the various tree formats (XML/HTML/Unix) to
  share more code. Probably make a generic tree crawling routine that calls
  various function pointers to emit the file information based on the kind
  of tree we want.

- Make wide character support less of a hack.

- Fully support HTML colorization properly.

- Go over the -R option for HTML output and make it cleaner & less of a hack.
  Should do -R internally so we don't have to rebuild a command line or use
  something awful like system().  Should be doable by saving some state and
  recursing and also separating out parts of main.

- Should probably make it so that options like -p, -u, etc print out info for
  the top directory, if people think that would be desirable.

- Might be nice to prune files by things like type, mode, access/modify/change
  time, uid/gid, etc. ala find.

- Just incorporate the stat structure into _info, since we now need most of
  the structure anyway.

Maybe do:

- With the addition of TREE_COLORS, add some custom options to perhaps colorize
  metadata like the permissions, date, username, etc, and change the color of
  the tree lines and so on.

- Make tree look for a .comments file in a directory and append the text from
  that file to the output of the files and directories, so that the output
  looks like Slackware's README file, like:

  > tree -F --comments
  ...
  |-- kernels/             Precompiled Linux 2.6.37.6 kernel images.
  |   |
  |   |-- hugesmp.s        The default standard install kernel for Slackware.
  |   |                    This supports pretty much everything in the
  |   |                    2.6.37.6 kernel, and includes support for Speakup.
  |   |                    This kernel requires at least a Pentium-Pro processor.
  |   |
  |   `-- huge.s           A single-processor version of huge.s that will
  |                        function with older hardware such as a 486 with
  |                        128MB (64MB _might_ work) or more of RAM.
  |                        This kernel also supports Speakup.
  ...

  Might be particularly nice for the HTML output, where the comments could be
  made as mouse-over popups or the like.

