Using a default Scalafmt config if none found

[guizmaii]

Hi,

I tried to use macrolizer in Scastie and in projects using Bleep as build tool and macrolizer was failing because it was not finding the .scalafmt.conf file

Could be nice to fallback to a default one instead of failing. That'd ease the use of this lib and would allow it to be used in contexts similar to Scastie

[sirthias]

Ah, yes. Good idea. Thank you!