Merge pull request #170 from LLFourn/proc_macro_arithmetic #709

Job	Run time
build	2m 0s
clippy_check	35s
Rustfmt	10s
doc-build	14s
test (x86_64-unknown-linux-gnu)	1m 44s
test-alloc (secp256kfun)	1m 10s
test (armv7-unknown-linux-gnueabihf)	5m 54s
test-alloc (sigma_fun)	34s
test-minimal (secp256kfun)	1m 13s
test-nightly	1m 29s
test-alloc (ecdsa_fun)	52s
test-minimal (sigma_fun)	37s
test-alloc (schnorr_fun)	1m 8s
test-minimal (ecdsa_fun)	50s
test-minimal (schnorr_fun)	1m 1s
	19m 31s

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