File format lacks comments

The pcb file format lacks a provision for comments. Two
types of comments should be added to both pcb files
and element files:

Simple file comments:
   // This is a comment
   // Generated by protel2pcb
These comments will not be preserved across edits.

Comment objects:
   Element[....]
   {
        Comment["Footprint copyright 2004 by John Doe"]
        Comment["element_filename='foo/bar/baz'"]
        Comment["vendor[0].name='digikey'"]
        Comment["vendor[0].part_no='500K-ND'"]
        Comment["vendor[0].price='$2.50']
        Comment["stencil_thickness=10mils"]
        Comment["height=5mm"]
        Comment["hole_tolerance={plus=10mils,minus=5mils}"]
        ....
   }
These comments will not be displayed in the editor
(unless someone wants to add a dialog box later) but
will be preserved across edits.

These objects could occur:
  - Inside an element in an element file
  - Inside an element embedded in a board file
  - Elsewhere in an element file

For compatibilty with older tools that read pcb files, one
could always use:
   cat file.pcb | fgrep -v "Comment[" | egrep -v "^//"
to strip off both types of comments.