Merge pull request #814 from adria0/fix/mdbook #4038

Job	Run time
Build target wasm32-unknown-unknown	3m 56s
Test on i686-unknown-linux-gnu	15m 46s
Test on ubuntu-latest	9m 21s
Bitrot check	1m 30s
Test on i686-unknown-linux-gnu with beta features	15m 12s
Test on windows-latest	12m 11s
Test on i686-unknown-linux-gnu with nightly features	17m 41s
Build target wasm32-wasi	3m 53s
Test on macOS-latest	11m 13s
Book tests	3m 38s
Test on ubuntu-latest with beta features	9m 30s
Code coverage	21m 15s
Intra-doc links	3m 39s
Rustfmt	12s
Test on windows-latest with beta features	12m 9s
Test on macOS-latest with beta features	14m 57s
Test on ubuntu-latest with nightly features	10m 26s
Test on windows-latest with nightly features	13m 32s
Test on macOS-latest with nightly features	11m 49s
	3h 11m 50s

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