Tag and release 0.2.0

[crsaracco]

Left to do for this release:

• Change signature of get_mut method on Outputs to fix unsafety bug
• Run cargo fmt and add a check in CI
• Add CI checks for Clippy
• Adjust some obsolete comments
• Update the changelog for 0.2.0
  • Among other things, make sure the major (thread-safety) changes are noted here
• Update Cargo.toml and dependency example in README.md to 0.2.0.
• Create a git tag for v0.2.0
• Release to crates.io (automatically done when creating tag)

Optional:

• remove api::events_raw()
• Update crate dependencies
• Document the major (thread-safety) changes in 0.2.0 somewhere other than the changelog?
• Change AtomicFloat and ParameterTransfer to use AtomicU32 for the f32 values, now that it is stable.