JanetRS v0.5.0

Changes

• BREAKING: Rename JanetClient::with_default_env ->
  JanetClient::load_env_default
• BREAKING: Rename JanetClient::with_replacements ->
  JanetClient::load_env_replacements
• Add catch arg to janet_fn attribute macro that adds code to catch Rust
  panics and transform them into Janet panics
• Add two new functions to initialize JanetClient:
  JanetClient::init_with_replacements and JanetClient::init_with_default_env
• Add JanetFile::temp
• Fix tuple::{IntoIter, Iter}::size_hint implementation
• Migrate to Rust 2021