[fitsbits] BINTABLE convention for >999 columns

[THIERRY FORVEILLE]

> Your suggestion does indeed increase the number of possible columns in a
> FITS table from 999 to 18574. But the fundamental problem still remains:
> there is a hard limit which will probably be reached for some applications.
> 
> Just as a fresh brainstorm, what do you think about this convention:
> removing the exact column identifier/number from the keyword name and
> instead relying on the keyword ordering. This will allow a
> (theoretically) unlimited number of columns, but will just rely on the
> order the keywords in the header (for each class/property, for example
> `TFORM' or `TTYPE').
> 
Order-independence of the interpretation of the keywords is deeply ingrained
into FITS. I don't think such a change would be acceptable, even if you'd
be addressing an immediately relevant limitation rather than a potential
one.