move to allocating c strings from rust

src/common/compat_rust.c

src/common/compat_rust.h

src/common/include.am

src/or/main.c

src/rust/Cargo.lock

src/rust/tor_allocate/tor_allocate.rs

src/rust/tor_util/Cargo.toml

src/rust/tor_util/ffi.rs

src/rust/tor_util/lib.rs

src/rust/tor_util/rust_string.rs

src/rust/tor_util/tests/rust_string.rs

src/test/include.am

src/test/test.c

src/test/test.h

src/test/test_rust.c

src/test/test_rust.sh