SD -> CAN conversion tool

It would be nice to have a tool that converts SD files into CAN strings, applies the skip checks in verify_can.process_record, and

  • if it passes, yields the new CAN string
  • otherwise, yields an error message

API design:

Add the action generate-can-ext which does a similar job as generate-can, but produces an output in the following format:

n1ccc(cc1)/C=C/c1ccncc1.Oc1cccc(c1)O    ABEKUN
<nocoords>    RESORA01
<invcan>    BRURAC10
<panick>    MUBJAU

I know that using < and > seems a bit usgly and ad-hoc. This is safe however, as the smiles specification does not contain these characters, making these strings unambiguous.