1. add .editorconfig file, add rules for .sh .bash files.
2. add make fmt target, use:
- gofmt *.go.
- shfmt *.sh *.bash, shell/completion.bash, shell/key-bindings.bash
need a left indent due to an outermost if block.
3. add shfmt check for bash scripts in make lint target.
4. install shfmt in actions.
