Handle SyntaxErrors after new-lines specially

In some cases, when we handle SyntaxErrors we need to ensure that the
column number is correct for a 1-indexed report. In some cases, we also
need to account for the fact that the SyntaxError has happened "after" a
new-line. To extract and alter the row and column numbers, we've moved
the logic to a private static method on the FileChecker object to avoid
an overly complex method.

Closes #237