[Groff] tbl: <T> and (T) as tab

[Bernd Warken]

Dear friends,

I got 2 interesting books about troff of theyear 1987. Especially two
2-char collections in tbl-parts are useful.  These collections become
the meaning of tab chars for cell jumping.

1) Sandra L Emerson, Karen Paulsell - troff TYPESETTING for UNIX(TM) Systems 
(1987)
This book seems to come from System V.
It documents that "(T)" has the meaning of a tab char for cell jumping.

2) David Barron, Mike Rees - Text Processing and Typesetting with UNIX (1987)
It documents that "<T>" has the meaning of a tab char for cell jumping.

So far, groff does not use these.  With these additions the line with
tab(...); is no longer necessary.

I have now trouble with C++.  So could someone else try to add these
character combinations to the .cpp files in src/preproc/tbl?

It might be possible, to allow also strings in the tab()-line as a first
step, instead of now only single character methods.

Bernd Warken