Supply three files to this form: an old file, a new file, and the revision
file that your createRevision function produced from the old and
new file. This will check that the revision file is validly formatted
according to the spec and that when the revision file is applied to the old
file by our correct revise function, it produces text
that is identical to the new file.
When the contents of the files are displayed by this checker, a space character will display as a space, a tab character will display as →, a carriage return as ∠, a linefeed/newline as ↓, and a non-printing or non-ASCII character as ∩.