Update get_attribute_ref prototype to return bit width of attribute.
Pass bits pointer to get_attribute_ref in nqp.ops.
Update (functional) implementors of get_attribute_ref to return bit-width.

Right now they are hard-coded to just return 8*sizeof(void *). I think that
should be a good way to return the number of bits in a machine word, but
probably a decision that deserves some more scrutiny.
Return correct number of bits in get_attribute_ref in CStruct.c.
Turns out Parrot #defines ALIGNOF, so no need to redo it in CStruct.c.
Handle bit widths in nqp.ops.
Add align field to storage_spec.

Also, adds initialisation of align field to all REPRs (and initialises a
couple of bits fields that weren't).
Merge branch 'master' into dyncall-sized-num
Update code to use Parrot's new ALIGNOF1.
Fix .align of P6bigint storage spec.
Start implementing compose protocol for P6int REPR.
Merge branch 'master' into dyncall-sized-num
Update P6opaque and NQPClassHOW to use new compose protocol.

The old protocol was a list of attribute infos, but the new protocol is a
hash, and that bit of info belongs in the attribute key of that hash, so fix
that.
Bump serialization format version.
First shot at sized int support in P6int.
Update CStruct to new way of doing things.
Fix two brainos.

One in P6int.c; if you're gonna reset the bit value to the default just before
returning, you're gonna have a bad time.
Another in CStruct.c; ensuring proper alignment wasn't done properly.
Refactor get_attr_{int,num} (which comes in two variants).

They shared some code that takes a pointer and a number of bits and
dereferences the pointer as an appropriately sized int/num, so refactor those
bits to shared functions.
Kill a piece of dead code.
Refactor how get_attribute_ref works.

Now, get_attribute_ref works more like at_pos_ref, by way of
get_attribute_stable (a new function), so that decoding pointers to embedded
type is delegated to the relevant type, rather than done in nqp.ops. This
eliminates the need for get_attribute_ref to return the number of bits in the
type to the caller via an inout parameter.

Also, this commit temporarily breaks sized int support in CStruct.