Introduce some shortcuts for the frequent commands

- [x] `+ <time>` instead of `+<time>`; same for `-`; the `+/-` operation as shortcut for `set`
- [x] `gtm push --tag` or smth like this for `gtm push && git push --tag`;
- [ ] `gtm #42` instead of `gtm switch 42`; and may be `gtm #` for `ghi list`;
- [x] `gtm note "message"` for `git commit --alow-empty -m "message"`;