Git discipline may have dropped at bit...

* Only two-sample liner model (i.e. Student's t-test)
* Rank by log fold change difference
* Specification of for time simulation dataset
* New status.py script
* Calculate log normalised counts for the endothelial dataset
* Add rankby_abs to scanpy
* Add pval.type = "some" to scran

Other small changes

and detlete zero p-values file