EditorConfig

Can we use [EditorConfig](https://editorconfig.org/) to pass `-y 'defaultIndent: "..."'` to `latexindent`? (See also #22.) To this, we need to extract the values of `indent_style` and `indent_size` for target files, which may be difficult for POSIX shell script if the section is written with brace expansion notation:
```editorconfig
[*.{tex,sty}]
indent_style = space
indent_size = 4
```