- Check Object Mode is either EDIT or OBJECT as appropriate.
- Change If loop to check command values - error if D, E, For M commands.
- Remove surplus command check in command_maths function.
- Added import of exceptions file.
- Check for Mesh Objects in Object or Edit Mode first and exit with error
  message if not.
- Some minor changes for obscure failures in unusual circumstances.
- Fixes and changes to code to correct minor errors and remove unnecessary
  checks.
- Refactored Command File structure.
- Add more checks to Fillet Operation to check selection and make sure
  current selected vertices/edges are always used. Previous version could
  use wrong selection if Bmesh SelectHistory was in place for Faces, or Edges.