Correct bin offset

[NickDraper]

Moves the bin boundaries by a user supplied offset

parameters
- Workspace (input/output)
- Bin offset (double) – can be negative

This will then add that offset to each bin.

Care should be taken not to end up with duplicate X vectors caused by simple adding through the cow_ptr. Perhaps you could check that the current X array is the same as the last one and then have them point to the same new vector.

[NickDraper]

This issue was originally trac ticket 246