Initial expression in dataset name implementation
Expand scalars and chop arrays with composite expressions
Fix warning when plotting log images
Use dataset expression for Image widget
Do not give undefined dataset error if dataset name matches python identifier
Use expression in linked_datasets examples to help testing
Rename DatasetOrFloatList to DatasetExtended. Move more things to using it.
Restructure code for dataset evaluation to avoid duplicaiton. Preserve 2D coordinates.
Add vcentre line step type
Add histogramming example
Update README
Add dsexpressions self test
More readme changes
Manual updates