Hamstercage

The sub-command `tag add` was not working correctly.

Update dependencies to current versions.

Instead of using the `-t` parameter, require the specification of the tag for the `add` and `remove` commands.

Target paths were handled inconsistently, leading to errors when saving or applying the manifest.

In the manifest, the entries always start with a slash (`/etc/motd`); when applying or saving, these are interpreted relative to the target directory (`--directory` parameter).

When specifying files on the command line, the path is normalized:
* `/etc/motd` and `etc/motd` are interpreted relative to the target dir for accessing the target, and applying to the manifest entry `/etc/motd`
* `/my/target/dir/etc/motd` (with `--directory /my/target/dir`) is interpreted as applying to the manifest entry `/etc/motd`

This release moves the documention from the README.md to the [website](https://hamstercage.io/).