* [env] remove crate-level re-exports for the hash module

* [env] rename ink_env::println -> debug_println

This makes the usage intent clearer.

* [lang] remove deprecated method

* [lang] hide all definitions that are only needed for codegen purposes

* [lang] remove False, move True

* [lang] remove unnecessary where bounds

* [lang] add EnvAccess forwarding for built-in crypto hashes

* [README] add ink_lang doc link

* [env] fix on-chain compilation

* [lang] apply clippy suggestion