len [label]
sets label = size of most recently linked/imported file
pos [label]
sets label = size of current segment. If no label, resets the position variable to 0.
label is added to the symbol table as an absolute entry.
Testing in merlin 16+, these are absolute entry labels, not gequ labels
Merlin does not include any ds fill in the len/pos, but that decision
seems questionable. these do include a ds fill for both.
