The source code has been through a rather complicated journey, and
it's occasionally useful to understand this history from CVS to a
private Subversion repository to its current location in git. So
document this more thoroughly, and ensure that everyone involved
is in the THANKS file.
De-emphasise the package management aspects, since these days
almost everyone prefers to use modern package managers such as
rpm / dpkg / Nix for (system-wide) package management.
Also include more popular modern use cases for Stow such as management
of dotfiles and software compiled in the user's $HOME directory.
Fixes#22: https://github.com/aspiers/stow/issues/22
