v0.3.0-beta.0

Notable changes since v0.2.0:

• Add rootlesskit --disable-host-loopback (requires slirp4netns v0.3.0 or VPNKit)
• Add rootlesskit --cidr (requires slirp4netns v0.3.0)
• Add rootlesskit --port-manager=(socat|slirp4netns|builtin)
• Add rootlessctl (API client)
• Add rootlesskit-docker-proxy (drop-in replacement for docker-proxy)