Support EditorConfig as inputs

[toastal]

I would like to see EditorConfig be used as a fallback for the default spacing when no format values are specified.

Advantages: keep indentation config in one place; no desync in config/execution; no need to pass arguments or override; ability to specify different values for different files/directories if needed for vendored third-party files

Disadvantages: requires parsing .editorconfig, a third-party format & would incur additional dependencies; minor endorsement of EditorConfig as a project since it would get special support

See response: kdl-org/kdl-rs#96 (comment)

[hougesen]

Good idea!

#55 added support for specifying indentation level using a custom kdlfmt config file. Adding fallback support for editorconfig should be pretty straightforward 😄