Get as close as possible to the original Elm compiler output and how
Parcel v1 displayed the errors:
- add some useful formatting
- disable the stack track (not useful when developing)
- convert structured elm errors report into Parcel's diabnostics
  structure
- preserve indentation in lines where parcel removes spaces (by using >
  as first char, it's a workaround but better than no indentation)

…mpiler-error-output

…ces, leave leading ones untouched

…ophP/parcel into improve-elm-compiler-error-output