Tests

Merge pull request #201 from LLFourn/siganture-share-newtype #845

Job	Run time
test (x86_64-unknown-linux-gnu)	4m 2s
test (armv7-unknown-linux-gnueabihf)	7m 10s
clippy_check	41s
doc-build	25s
build	2m 22s
Rustfmt	12s
test-alloc (secp256kfun)	1m 9s
test-minimal (secp256kfun)	1m 9s
test-nightly	2m 16s
test-minimal (sigma_fun)	1m 6s
test-alloc (sigma_fun)	2m 47s
test-minimal (ecdsa_fun)	3m 4s
test-alloc (ecdsa_fun)	47s
test-minimal (schnorr_fun)	1m 38s
test-alloc (schnorr_fun)	1m 14s
	30m 2s

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