[developers] comments inside definitions and clean up of tdl input code

[Ann Copestake]

I have added a limited facility to put comments inside definitions of types,
rules etc in the TDL file.  The limitations are:

a) comments must be introduced by a semi-colon ; - the #| notation is
not supported in definitions.

b) comments are only allowed after the preliminary parts of the
definition (after the parents in type definitions).  

c) comment characters are only allowed at the begiining of lines (this
isn't enforced - they may work elsewhere - but I've only tested them
in places where a line break seems feasible)

d) the "comment" syntax is still available: comments expressed like
this are stored by the system and (potentially) available for
interactive help etc.  The ; comments are just junked.  ; comments
should follow the "comment"s.


I have also purged the tdl input code of various defunct stuff that
dated back to the days when we were trying for PAGE compatability.
This includes templates introduced by @, status commands etc.  It is
possible that some very old grammars still in use may fail to load.
However, I don't think I have removed anything functional - hence any
such grammars could have the non-accepted pieces removed without
change to functionality.  

As always, let me know of problems.

Ann