cargo

histogram: add subtract operation for sparse histograms #420

Job	Run time
audit	13s
clippy	26s
build-ubuntu-latest-release	46s
check-ubuntu-latest	32s
build-ubuntu-latest-debug	34s
rustfmt	6s
check-macos-latest	36s
build-macos-latest-release	1m 0s
check-windows-latest	2m 21s
build-macos-latest-debug	46s
build-windows-latest-release	3m 41s
build-windows-latest-debug	2m 24s
clippy-upload	12s
verify all tests pass	1s
	13m 38s

Provide feedback