Change to header specs

[Roland Melkert]

I'm ok with it in principle but would suggest changing:

The use of '~' for part files is at the author's discretion, to hide mouldings that are not released independently. This is one case where merely reading the LDRAW_ORG line is insufficient for tools to know how to treat the file.

to

The use of '~' for non "s\" part files is at the author's discretion, to hide mouldings that are not released independently. This is one case where merely reading the LDRAW_ORG line is insufficient for tools to know how to treat the file.