This program reads a given markdown file, collects other linked markdown files,
converts them all to html using a template, and replaces the markdown links
to point to the corresponding html files.
The options are as follows:
-destdir dir - Destination directory to write all resulting files to, defaults to the same directory as the source file
-assetdir dir - Directory with additional files to copy to the destination directory, unset by default
-tmplfile file - Template file to use, defaults to template.html