Spec binary format

[rossberg]

Note: this does not yet take #372 into consideration, i.e., uses the temporary opcodes for now.

[jakobkummerow]

Is it intentional or an oversight that this PR disregards #372 and the discussion that happened there?

Also, instructions.rst line 103:

:ref:`Reference instructions <syntax-instr-ref>` are represented by single byte codes.

is now outdated (since it's an unmodified line, the review tool won't let me put a comment there).

[rossberg]

Is it intentional or an oversight that this PR disregards #372 and the discussion that happened there?

Since that isn't resolved yet, but I wanted to make progress with the spec, I did it based on the old opcodes for now. It's easily changed once #372 is finalised.

:ref:`Reference instructions <syntax-instr-ref>` are represented by single byte codes.

is now outdated (since it's an unmodified line, the review tool won't let me put a comment there).

Thanks, updated.

[tlively]

largely rubber stamp lgtm