ENH: add ITstream append and seek methods.
- ITstream append() would previously have used the append from the underlying tokenList, which leaves the tokenIndex untouched and renders the freshly appended tokens effectively invisible if interspersed with primitiveEntry::read() that itself uses tokenIndex when building the list. The new append() method makes this hidden ITstream bi-directionality easier to manage. For efficiency, we only append lists (not individual tokens) and support a 'lazy' resizing that allows the final resizing to occur later when all tokens have been appended. - The new ITstream seek() method provides a conveniently means to move to the end of the list or reposition to the middle. Using rewind() and using seek(0) are identical. ENH: added OTstream to output directly to a list of tokens --- BUG: List::newElem resized incorrectly - had a simple doubling of the List size without checking that this would indeed be sufficient for the requested index. Bug was not triggered since primitiveEntry was the only class using this call, and it added the tokens sequentially.