This also allows `Instruction` to be `Copy`, which massively speeds
up `<Instructions as Clone>::clone` since it can now just `memcpy`
the bytes using SIMD instead of having to switch on every single
element. I haven't looked at the disassembly of `InstructionIter::next`
yet, it could be that there are even more improvements yet to be gained
from either:
* Only doing work on `BrTable` (this might already be the case depending
on the whims of the optimiser)
* Using `unsafe` to make it a noop (we really don't want to do this,
obviously, since it means that `Instructions` has to be immovable)
* Hide Instructions implementation behind an iterator
* Hide instruction encoding behind isa::Instructions::push()
* Consistently use u32 for program counter storage
* Refer to instructions by position rather than index
* Define Instruction Set.
* WIP
* WIP 2
* Tests
* Working
* Bunch of other tests.
* WIP
* WIP
* Use Vec instead of VecDeque.
* Calibrate the limits.
* Clean
* Clean
* Another round of cleaning.
* Ignore traces.
* Optimize value stack
* Optimize a bit more.
* Cache memory index.
* Inline always instruction dispatch function.
* Comments.
* Clean
* Clean
* Use vector to keep unresolved references.
* Estimate resulting size.
* do refactoring
* Validate the locals count in the begging
* Introduce Keep and DropKeep structs in isa
* Rename/Split Validator into Reader
* Document stack layout
* Remove println!
* Fix typo.
* Use .last / .last_mut in stack
* Update docs for BrTable.
* Review fixes.
* Merge.
* Add an assert that stack is empty after the exec
Jef
Will Glynn
Sergey Pepyakin
Wei Tang