add utilities to automatically compute a working mapping by only specifying SDOs

[jimy-byerley]

For what regards slave's control, there will be objects, each responsible of the control of a part of the machine, using parts of the process data matching the relevent SDOs of relevant slaves.
However

• multiple such objects might share the same SDOs (for reading mostly)
• multiple such objects might ask SDOs that are all in the same PDOs

Because of these facts, it would be sub-optimap to let each object create its own mapping on each slave. mapping should be decided once all SDO needs of all control objects have been taken into account.
An automatic mapping utility is thus necessary, allowing control objects to request for their SDOs and then once the mapping is done, simply access them.

This should ressemble to to following for the end-user:

let mapping = AutoMapping::new()
mapping.require(Sdo::<i32>::complete(0x1234))  // in control-object: request a SDO in the global mapping
let mapping = mapping.solve(infos)
let position = solution.request(Sdo::<i32>::complete(0x1234)) // in control-object: retreive its Field in the logical memory