* swg links path/to/page
  Prints all (internal) links presented on the page.
* swg backs path/to/page
  Prints all (internal) backlinks to the page.
* swg cats [prefix]
  Print all categories/directories, optionally filtered by prefix.
* swg htmls path/to/dir
  Render current directory to a bunch of HTMLs.
* swg dot | dot -Tpng >relations.png
  Generates Graphviz'es dot graph with internal links relationships.
* swg info >out.info
  Generates GNU Info output.
* swg latex >out.tex
  Generates LaTeX output.

If directory does not have "index" file, then it will be autogenerated
with all files in the directory (category) and all backlinks to it.

If $SWG_DO_BACKS=0 environment variable is set, then no backlinks table
will be generated on the pages by default.

.swgignore may contain regular expressions (one per line) to ignore
specified files during processing. Your directory may contain images or
binary files, that must not be processed. Files starting with dot will
be ignored by default.

If $SWG_PRINT_MISSING environment variable is set, then warning will be
print for links leading to non-existent pages.

If $SWG_DO_SRC=0 environment variable is set, then no links and source
pages will be generated. Pure HTML output.

How to forcefully change the title of the generated HTML page?
Use sed/perl to replace "<title>..." line in it.
