Feature/eds parse factor and description

[marcovannoord]

For my work, i needed to use the Factor and Description, that already seem to have been implemented CANopen. However, they were currently not/never set by an EDS-file.
I added parsing for the Factor and Description, and i have added some unit-tests for them.

[marcovannoord]

According to the CanOpen specification, there is room to add these tags:

If not specified otherwise, all sections and entries in this paper are mandatory. In order to support future extensions it is allowed to include additional sections and additional entries inside the sections. Anyhow the Conformance Test Tool will recognise this with warning messages

If not used, or when set to default, they will not be exported, to prevent any changes to current implementations

[unsanded]

I agree that this would be a nice addition, because it feels kind of weird to always use var.raw instead of var.phys. And it would also prevent errors.

[marcovannoord]

@christiansandberg What is your opinion about this MR?

[christiansandberg]

Sorry for the delay. I think it makes sense to be able to specify it. Not sure what the EDS spec says about custom attributes but it should be OK.