Update documentation

* workflows/bio/variation.workflow: Update docs
* snakemakelib/report/picard.py: Add ID to fieldnames and metrics; non-functional!
* snakemakelib/report/picard.py: remove ID from metrics, fieldnames. remove EXTENSIONS
Add SI suffix formatting
* snakemakelib/report/utils.py: new; subclass string.Formatter to format SI suffixes
* test/test_utils.py: add test for utils module