Add inter-lane operations

[penzn]

Change by Florian Lemaitre, orgially made in PR #27:

https://github.com/WebAssembly/flexible-vectors/pull/27

[penzn]

@lemaitre, I took the committer from first commit in #27, but it does not point to your GH account for some reason. Let me know if you want to change it.

Also, the instructions can be characterized as follows:

• [ ] Lookup (aka shuffle)
• [x] Broadcast of a lane: #29
• [ ] Lane shifts (different style)
• [x] Interleave, odd and even: #30
• [x] Concat, odd and even: #30

[lemaitre]

I think the first commit is not linked to my github account because I made it locally, not from github, and I might have put the wrong email. I will check, and if that is the case, I will force push my branch.

[lemaitre]

Confirmed, I messed up the email. Now I have properly set the email (and took the time to set up pgp signature). So if you rebase your branch, you should be fine.

[penzn]

That looks better now :)