Subscripts and sizes should be signed (redux)

[tczajka]

@T4r4sB

Rust developers have not heard of the Stroustrop article: https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1428r0.pdf , they haven't heard of the experience of a C++ programmer (never use unsigned numbers until you really need bit representation and bitwise operations), and still use dangerous unsigned types that can cause your program to crash with simple subtraction.

Previous discussion about this.