Unify our bytepointer representation in the libraries

[marijnh]

We currently have sbuf, *u8, and *void, which hampers interop somehow. I think sbuf can be thrown out altogether. *void used for 'raw memory holding whichever', and *u8 for stuff that's explicitly a buffer of bytes or characters.

[graydon]

Agreed. Sbuf is vestigial from when we didn't have unsafe pointer types.

[marijnh]

Actually, sbuf is a synonym for *u8 now (I thought it was still a native type). Closing this in favour of #1715.