This change makes PositionedComment and ParseNote contain end columns.
It additionally modifies the JSON formatter to show the end column in an
"endColumn" property. No modifications to the messages shown by any
other formatter have been made.
Currently, all checks set the end column to the start column. It should
now be possible however to start setting the end column in the parser.
Additional work is needed to set the end column during AST analysis.
Russell Harmon
Vidar Holen
David Haguenauer