README: Remove outdated information
README: Convert to Markdown and apply cleanups

Use the Markdown format for the README file and apply various minor
cosmetic changes.
Remove the BUGS file

The BUGS file wasn't maintained properly anymore.  And doing so makes no
sense.  That's what the bug tracker is for.
README: Use code blocks for commands
Add symlink: README.md -> README

Add a symlink so that GitHub renders the README file as Markdown.
README: Apply another few cosmetic changes
README: Minor cosmetic change