Screen using SSS

[tdudgeon]

Create a component similar to the current rdkit/screen.py component , but that works using substructure search instead of similarity search.

Initially could take just a single structure as query (as smiles or molfile) but should be extended to allow multiple substructure queries to be specified as SDF or smarts file. The output would be structures matching any of the query structures. Thought will need to be given for how to record which input structure matches when generating the results.

screen.py should also be extended to handle multiple query structures.