bytecursor vs std-shims vs genio

`No-std` replacement for `std::io::Read`, `std::io::Write`, and `std::io::Seek`

A series of std shims to make alloc more feasible

A type safe, low level replacement for `std::io`. Supports `no_std` for embedded development, just disable cargo feature `std`. Because of limitations of `std::io::Error` type, `genio` provides `Read` and `Write` traits that allow implementors to choose their own type. This type can be better at expressing what kinds of error can happen.