OffsetPosition lineContents wrongly includes a newline

[inkytonik]

According to the documentation, the lineContents method of a Position should not include a newline, but this code:

def lineContents: String =
    source.subSequence(index(line - 1), index(line)).toString

includes everything from the start of line - 1 to the start of line thereby including the newline at the end of the line.

The effect of this bug is that messages that use Position.longString end up with an undesirable blank line between the contents line and the up arrow line since longString also puts a newline between the two:

LINE CONTENTS

      ^

Presumably the fix is to use index(line) - 1 in the above code instead of index(line) so that the newline is omitted.

[inkytonik]

Actually that fix will only be valid if the source ends in a newline.

[gourlaysama]

Fixed in #77.