Deprecate `group_by` in favor of `chunk_by` #754

Job	Run time
doc	12s
msrv	47s
check	18s
check format	3s
check (--no-default-features)	12s
semver-checks	2m 25s
test	2m 45s
check (--no-default-features --features use_alloc)	9s
check (--all-targets --all-features)	16s
All checks succeeded	0s
	7m 7s

Provide feedback