Vnet-manager

New feature:
- Support Netplan routes on machine interfaces (https://github.com/Erik-Lamers1/vnet-manager/pull/28, https://github.com/Erik-Lamers1/vnet-manager/pull/32, https://github.com/Erik-Lamers1/vnet-manager/pull/34)

Example configs:
- Add iBGP example config (https://github.com/Erik-Lamers1/vnet-manager/pull/33)

CI changes:
- Migrate away from Travis to Github actions (https://github.com/Erik-Lamers1/vnet-manager/pull/29, https://github.com/Erik-Lamers1/vnet-manager/pull/30, https://github.com/Erik-Lamers1/vnet-manager/pull/31)

New feature:
- Add bridge interfaces option to machine config (https://github.com/Erik-Lamers1/vnet-manager/pull/26)

Changes:
- Move argeparser to separate file (https://github.com/Erik-Lamers1/vnet-manager/pull/27)

Changes

- Added LXD preseed file for supported Ubuntu versions (https://github.com/Erik-Lamers1/vnet-manager/pull/24)
- Added type hinting to most functions (https://github.com/Erik-Lamers1/vnet-manager/pull/22)
- New version of [Black](https://github.com/psf/black/releases/tag/20.8b1) (https://github.com/Erik-Lamers1/vnet-manager/commit/2d8432ebdc9dee4599913eac1428cee92cf76cc4)

Major changes

- defaults.yaml is no longer needed, all provider settings are now loaded from the Python settings: (https://github.com/Erik-Lamers1/vnet-manager/pull/20)

Minor changes

- Shutdown base machine if DNS check fails (https://github.com/Erik-Lamers1/vnet-manager/pull/14, by ppartarr)
- Documentation updates (https://github.com/Erik-Lamers1/vnet-manager/pull/15, by SyntheticOxygen)
- Test coverage no longer covers the tests themselves (https://github.com/Erik-Lamers1/vnet-manager/pull/21)

This release changes two things:

- `defaults.yaml` is now excluded from the `list` action. This gets rid of the nasty error messages when vnet-manager tried to parse the `defaults.yaml` config, while it couldn't.
- The host machine type will now explicitly disable IP forwarding on creation.

This release introduces two new features

- The `--no-hosts` option made by tim427. When this option is passed VNet-manager will not generate the `/etc/hosts` file for any machines. This can be handy when testing some mDNS or other auto-discovery protocols/programs.
- IPv4 is now optional for machine interfaces.

Also, the (example) configs in the `config` directory are now checked for proper YAML syntax by the CI and `tox`.