Git-machete

- added: `addable` category of `list`
- added: `advance` command
- added: `machete-post-slide-out` hook
- added: support for `GIT_MACHETE_EDITOR` env var
- changed: `go root` no longer raises an error when the current branch is root
- fixed: `show root` no longer raises an error when the current branch is root
- fixed: Bash completion for `-y` option in several commands
- fixed: handling the case of current directory becoming non-existent (e.g. as a result of checkout)
- improved: `add` accepts remote branches as well (just like `git checkout`)
- improved: `discover` limited to ca. 10 most recently checked out branches by default
- improved: `discover` skips merged branches for which no child branches have been inferred
- improved: release process has been simplified

- added: `--as-root` option to `add`
- added: `--branch` option to `anno`
- added: `is-managed` plumbing command
- added: `current` subcommand to `show`
- added: animated gif to README + script for generating gifs automatically
- improved: formatting of help, prompts, logs, warnings and other messages
- fixed: help for a few existing commands

- fixed: remove reviewer setting when opening a PR to NixOS/nixpkgs
- changed: confinement of snaps from `strict` to `classic`
- changed: Docker images moved from under `virtuslab` organization to `gitmachete`
- changed: `apt-ppa` in all contexts to `deb-ppa`
- improved: determining the default editor (also including `git config core.editor`, `$GIT_EDITOR`, `editor` and `$VISUAL`)

- fixed: build of rpm package
- improved: organization of deployment stages on CI

- fixed: minor release-related issues
- fixed: interactive input for `traverse` in case of an untracked branch

- added: support for Snappy
- added: script for creating an annotated tag for release
- added: extra checks in CI
- added: release guidelines
- fixed: implementation of backup of .git/machete file in `discover`