Add a macro to make initialization easier #269

Job	Run time
test	46s
check (thumbv7m-none-eabi, nightly)	22s
check (thumbv6m-none-eabi, stable)	20s
check (thumbv6m-none-eabi, nightly)	21s
Clippy	20s
check (thumbv7m-none-eabi, stable)	17s
Format	15s
rustdoc	16s
	2m 57s

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