Add --pretty option to futhark.
Add --pretty option to futhark.

ihc/futhark,ihc/futhark,diku-dk/futhark,diku-dk/futhark,HIPERFIT/futhark,diku-dk/futhark,diku-dk/futhark,HIPERFIT/futhark,HIPERFIT/futhark,ihc/futhark,diku-dk/futhark