Lots of fixes.

Fixed a bug where Sequence length was stored inaccurately. Made Sequence::merge call the appropriate methods. Sequence
equality operator now checks if the length is equal before comparing anything. Fixed a bug where initial_sequence would
not iterate over all options for f2. WordToken now stores heap pointers in its list of Sequences, so that it's always
ensured it points to the same Sequences if the WordToken is copied.