* Upgrade all crates to the Rust 2021 edition
I've personally started using the new format strings for things like
`panic!("some message {foo}")` or similar and have been upgrading crates
on a case-by-case basis, but I think it probably makes more sense to go
ahead and blanket upgrade everything so 2021 features are always
available.
* Fix compile of the C API
* Fix a warning
* Fix another warning
This is the test-programs crate, which builds and runs whole programs
compiled to wasm32-wasi.
To actually run these tests, the test-programs feature must be enabled, e.g.:
cargo test --features test-programs/test_programs --package test-programs