Release v2.2.0

- Add working examples for cfgmatic-source (basic, file_source)
- Add working examples for cfgmatic-reactive (basic, subscriptions)
- Add criterion benchmarks for cfgmatic-merge

- Fix clippy warnings in examples and production code
- Fix broken doc links in cfgmatic-merge (MergeError variants)
- Fix cfgmatic/src/lib.rs code block syntax error
- Make async_multi module conditional on 'async' feature in cfgmatic-loaders

- Add dispatcher tests in cfgmatic-reactive
- Update READMEs for cfgmatic-source and cfgmatic-reactive
- Remove unused code and fix dead_code warnings
- Add clippy allow attributes for pedantic lints in active crates