Use doubling strategy for allocating memory in ragged columns?

[jeromekelleher]

In #1683 we updated the default strategy for allocating memory for the fixed size table columns to use doubling.

Should we do something similar for the ragged columns like metadata? It's probably what an API user would expect I think. We should also document the tsk_individual_table_set_max_metadata_length_increment etc methods so that power users can keep control of memory, if they want to.

[benjeffery]

Yep, thanks for this. I had thought it while coding up the rows changes and forgot to make an issue.