Many unsafe memory operations

[evmar]

This project does a lot of pointer-fiddling casts and dereferences that may violate memory safety. In many cases I am still figuring out the right interface to model memory etc., see issues like #23 and #26, and worrying about safety additionally isn't useful yet.

I would like to fix them someday. Per Rust they are all in "unsafe" blocks and easy to grep for. I created this bug just to fold others into it.

[evmar]

$ git grep 'unsafe {'  | wc -l
     126