Version mismatch

[mre]

I noticed that we released 0.7.0, which should technically have been 0.6.3. My bad, sorry.
To avoid confusion, I propose to skip 0.7.0 on crates.io and go straight to 0.8.0 on crates.io (i.e. in the Cargo.toml) and on GitHub releases.

It might be fine because we added quite some additional functionality lately, namely illegal opcode support in #126 and interrupt handling in #122, which merits a feature release.

@omarandlorraine what do you think?

[omarandlorraine]

That seems reasonable, let's bump the version number to 0.8.0.