COMPONENTS OF is almost working

[vanrein]

Got most of COMPONENTS OF working:

• generation of DER_PACK_ and DER_PIMP_ is working
• generation of DER_OVLY_ does not

The matter is how to get to the structure elements. Already added a default-False parameter naked that can be explicitly set to naked=True to unleash elements in a structure without the opening struct { and closing }.

[vanrein]

Note issue #17 in which we realised that using DER_PIMP_ is no longer good, now that it got parameterised and simply adding the outside layer with changed tagging.

We'll have to generate DER_COMP_ to do the skip-one if we need to. Ah well, it's only definitions anyway, no space consumed.