 - handle repeated IEs
 - q_assign should remove old value (i.e. zero destination)
 - bit numbering is wrong; should be <size@high>
 - should be library (well, need at least more flexible name selection)
 - copies of adjacent fields should be merged
 - copies of partial bytes should be byte-wide if rest is only zeroes
 - should be able to have multiple selectors in one byte
 - case/default needs better compile-time check
 - parser shouldn't copy unnamed fields
 - optimize
 - code needs a lot of cleaning


Restrictions
------------
 
 - there's only very limited error checking
 - no support for arrays (repeated IEs)
 - copy operations are not optimized
