[Rd] Experimental Rd parser in trunk.

[Duncan Murdoch]

A couple more comments on the \dots problem:

1.  Allowing {} after \dots is unsatisfactory, because the current 
parser will render the braces, i.e. 1\dots{}10 is rendered as 1..{}10.
I'd like to have enough back-compatibility that it is possible to 
rewrite a man page to work in either system.

2. I could change the rules for what ends a markup macro, to allow only 
alphabetic chars in one, so that 1\dots10 is legal again.  This would 
require changing or making exceptions for \linkS4class, \S3method, and 
\S4method, because they contain digits.  I think this would rule out 
ever creating macros \linkS or \S because of the ambiguity; the latter 
might be a worry.

So I'm still leaning towards adding \sp...

Duncan Murdoch