Merge pull request #196 from quartiq/split-mqtt #620

Job	Run time
audit	10s
compile (stable, thumbv7em-none-eabihf)	55s
documentation	18s
compile (1.65.0, thumbv7em-none-eabihf)	2m 10s
examples (mqtt)	33s
style	34s
test (stable)	32s
test (stable, --all-features)	35s
test (stable, --no-default-features)	32s
test (stable, --no-default-features --features json-core)	41s
test (1.65.0)	1m 41s
test (1.65.0, --all-features)	1m 42s
test (1.65.0, --no-default-features)	1m 44s
test (1.65.0, --no-default-features --features json-core)	1m 40s
	13m 47s

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