Calls to change_id(from, to) change the ensemble ID stored in the dabase.

- Tests now use Strings to tag ensembles
- Added tests for fit/int/root

- Native BDIO format also adds this option

After a proper configuration of the chunk size, ForwardDiff
outperforms hyperd basically always.

This commit stores the last version of hyperd.

Still some work required to avoid allocations in functions:
- uwerr
- basic Math operations
- addobs

Working and crosschecked:

  - Computation of Gamma(t), drho(t) without replica
  - Indexing and error propagation