Disambiguate "byte" size

[Rudxain]

The Glossary and "Type Layout" don't specify the size of a "byte".

• Was that intentional?
• Is it a real byte? (platform-dependent smallest unit of addressable memory?)
• Is it guaranteed to be an octet?

I think it's worth being explicit about that.

BTW, the bool reference seems somewhat contradictory:

• size_of::<bool>() == 1 implies platform-dependent byte
• The hexadecimal bit-patterns imply u8 (guaranteed octet)

Note

Previous discussions:

• Lint for the reserved ABI of bool rust#46176
• Document the size of bool rust#46156

IMO, bytes are more honest and correct than octets (for bool and some enums, at least). For primitives such as char and u8, and exact bit-count is better than bytes

[bjorn3]

I don't think we support any target where a byte is anything other than 8 bits, just like we don't support any systems that use something other than two's complement for signed integers.