- just uint32 and string iterators for now, those are the most common ones
- allows somewhat more convenient code constructs when type is known,
eg no need to separately check for non-null inside loops
- headerGet() returns even array data in a single allocation block, but
regular (string) arrays need to have the pointers in array freed too
- set immutable flag on header data
- formatPrefix already contains the padding, just use rasprintf() on that
to get properly allocated buffer without messing with it manually
- xml format doesn't honor padding anyway so don't bother with it
- rpmtdGetUint() for 16 and 32 bit integer types, similar to
rpmtdGetString() (equally usable with scalar types and arrays)
- rpmtdToString() which converts "any" header data into string presentation