Improve the documentation, the CI and fix Clippy #394

Job	Run time
Check all the features of the heed project (ubuntu-latest)	19s
Check the heed3 project (ubuntu-latest)	18s
Check the heed3 project (windows-latest)	2m 34s
Check the heed3 project (macos-latest)	20s
Check all the features of the heed project (macos-latest)	21s
Check all the features of the heed3 project (ubuntu-latest)	18s
Ensure clippy is happy on heed and heed3	21s
Check all the features of the heed3 project (macos-latest)	21s
Run the heed examples (ubuntu-latest)	1m 23s
Ensure the heed and heed3 project are formatted	11s
Run the heed examples (macos-latest)	24s
Run the heed3 examples (ubuntu-latest)	22s
Test the heed3 project (ubuntu-latest)	1m 7s
Run the heed3 examples (macos-latest)	24s
Test the heed3 project (windows-latest)	2m 2s
Test the heed project (ubuntu-latest)	30s
Ensure heed3 is not erasing heed	5s
Test the heed3 project (macos-latest)	36s
Test the heed project (windows-latest)	2m 47s
Test the heed project (macos-latest)	38s
	15m 21s

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