Using swizzle for some of the geometric product operations was a bit
clunky and has problems with alignment. While I will still need it in
the future, it turns out that the extend instruction almost did what I
needed. However, I'm unsure that reversing components within an extended
vector is the way to go.
The extend instruction is for loading narrower data types into wider
data types, eg, single element into 2, 3, or 4 element types, with a
small set of extension schemes: 0, 1, -1, copy (for 1->any and 2 -> 4).
Possibly most importantly, it works with unaligned data.
Progress towards #30
