Add 'whodunnit' to YML

@danmaclean This PR adds 'whodunnit' support to the YML, if available. For example:
```yaml
---
organism:
  Local name: Andy's Organism
  Genus: Arabidopsis
  Species: thaliana
  Strain: Col 1
  Pathovar: A
  NCBI Taxonomy ID: '3702'
  Last updated by: Andy Shipman
  Last updated on: 22 April 2013
```