Die in CStruct if native type isn't a multiple of 8 bits wide.
Make P6{int,num} robust when bits key is absent on REPR composition.
Set sensible zero values in CArray on out-of-bounds access.
Teach P6opaque how to align objects properly.
Teach P6opaque how to deal with odd (not multiple of 8) native bit widths.
Remove dead code from CArray.
Compute allocation strategy of CStruct on REPR compose.