Change how dotfiles symlinks are deployed

[ZeroKnight]

My current symlink deployment strategy ends up linking whole directories at a time, which has some problems:

• Since the symlink points to a directory in my local dotfiles repo, any additional configuration created externally dirties the work tree
• The deploy step fails when a directory in ~/.config already exists, e.g. systemd

I should probably move to a linking strategy where I link only files whenever possible instead. I may need to make some exceptions, but drilling down to the leaves and creating parent directories as needed seems very unlikely to be problematic.