Crubit rstd library

Disclaimer: This project is experimental, under heavy development, and should not be used yet.

This directory contains C++ libraries that help work with Rust types. For example, rstd::Char represents Rust's char type (a separate type from C++'s char32_t is needed to detect certain invalid bit patterns result in Undefined Behavior in Rust; additionally char32_t takes at least 32 bits, rather than exactly 32 bits).